Naphthyridine Derivatives as a Model System for Potential Lithium-Sulfur Energy-Storage Applications

Naphthyridines have been identified as structural elements in sulfurized polyacrylonitrile, which is a common electrode material in lithium–sulfur batteries. Some dibenzonaphthyridine derivatives with a fused dithiolo moiety were prepared as model compounds for battery studies. These heterocyclic systems were prepared via the corresponding diphenyldicarbamide intermediate. Followed by naphthyridione formation, stepwise installation of the dithiolane subunit occurred in a straightforward manner. In the solid state, the heteroaromatic system is completely planar and was thoroughly characterized. Initial battery cycling tests indicated a potential use of such structural motifs in sulfur–lithiu…

Novel electrolytes for electrochemical double layer capacitors based on 1,1,1,3,3,3-hexafluoropropan-2-ol

Abstract 1,1,1,3,3,3-Hexafluoropropan-2-ol (HFIP) was tested for its applicability as solvent in electrolytes for energy storage devices. A comprehensive characterization with respect to solubility, conductivity, as well as chemical and electrochemical stability was carried out with different conducting salts. Furthermore, different HFIP solutions containing standard supporting electrolytes and alkali metal fluorides, respectively, were applied in electrochemical double layer capacitor cells. Their behavior was studied with impedance spectroscopy and cyclic voltammetry at low scan rates and compared to the current benchmark electrolytes based on propylene carbonate (PC) and acetonitrile (AN…

ChemInform Abstract: Powerful Fluoroalkoxy Molybdenum(V) Reagent for Selective Oxidative Arene Coupling Reaction.

A novel dinuclear fluoroalkoxy Mo(V)-complex is efficient as reagent for the oxidative arene coupling of electron-rich arenes with superior reactivity compared to MoCl5 and MoCl5/TiCl4.

Developments in the dehydrogenative electrochemical synthesis of 3,3′,5,5′-tetramethyl-2,2′-biphenol

Abstract The symmetric biphenol 3,3′,5,5′‐tetramethyl‐2,2′‐biphenol is a well‐known ligand building block and is used in transition‐metal catalysis. In the literature, there are several synthetic routes for the preparation of this exceptional molecule. Herein, the focus is on the sustainable electrochemical synthesis of 3,3′,5,5′‐tetramethyl‐2,2′‐biphenol. A brief overview of the developmental history of this inconspicuous molecule, which is of great interest for technical applications, but has many challenges for its synthesis, is provided. The electro‐organic method is a powerful, sustainable, and efficient alternative to conventional synthesis to obtain this symmetric biphenol up to the …

Palladium-catalyzed domino C-H/N-H functionalization: an efficient approach to nitrogen-bridged heteroacenes.

Palladium-catalyzed domino C-H/N-H functionalization for the synthesis of novel nitrogen-bridged thienoacenes and 10H-benzo[4,5]thieno[3,2-b]indole derivatives from dihaloarene is reported. This domino sequence consists of initial C-H functionalization of the benzo[b]thiophene moiety, followed by Buchwald-Hartwig coupling. This transformation is also useful for the synthesis of highly π-extended compounds.

Aktive Anode auf Molybdänbasis für dehydrierende Kupplungen

Metal- and Reagent-Free Anodic C−C Cross-Coupling of Phenols with Benzofurans leading to a Furan Metathesis

Heterobiaryls consisting of a phenol and a benzofuran motif are of significant importance for pharmaceutical applications. An attractive sustainable, metal- and reagent-free, electrosynthetic, and highly efficient method, that allows access to (2-hydroxyphenyl)benzofurans is presented. Upon the electrochemical dehydrogenative C-C cross-coupling reaction, a metathesis of the benzo moiety at the benzofuran occurs. This gives rise to a substitution pattern at the hydroxyphenyl moiety which would not be compatible by a direct coupling process. The single-step protocol is easy to conduct in an undivided electrolysis cell, therefore scalable, and inherently safe.

Modern Electrochemical Aspects for the Synthesis of Value‐Added Organic Products

The use of electricity instead of stoichiometric amounts of oxidizers or reducing agents in synthesis is very appealing for economic and ecological reasons, and represents a major driving force for research efforts in this area. To use electron transfer at the electrode for a successful transformation in organic synthesis, the intermediate radical (cation/anion) has to be stabilized. Its combination with other approaches in organic chemistry or concepts of contemporary synthesis allows the establishment of powerful synthetic methods. The aim in the 21st Century will be to use as little fossil carbon as possible and, for this reason, the use of renewable sources is becoming increasingly impo…

Leistungsstarkes Fluoralkoxy-Molybdän(V)-Reagens für die selektive oxidative Arenkupplung

Wir stellen ein neues Fluoralkoxy-Molybdan(V)-Reagens 1, mit im Vergleich zu MoCl5 oder MoCl5/TiCl4 hoherer Reaktivitat und Selektivitat in der oxidativen Kupplung von Arenen vor. Haufige Nebenreaktionen wie Chlorierung und/oder Oligomerenbildung werden erheblich reduziert, sodass ein leistungsstarkes und nutzliches Reagens fur die oxidative Kupplung erhalten wird. Theoretische Untersuchungen der Wechselwirkung des Reagens mit 1,2-Dimethoxybenzol-artigen Substraten deuten auf einen Innenspharen-Elektronentransfer gefolgt von einem radikalkationischen Reaktionspfad fur den oxidativen Kupplungsprozess hin. ESR-spektroskopische und elektrochemische Untersuchungen, Rontgenkristallstrukturanalys…

Convenient Synthesis of 3-Cinnamoyl-2-styrylchromones: Reinvestigation of the Baker-Venkataraman Rearrangement

An efficient and straightforward, one-pot sequence gives access to highly functionalized 3-cinnamoyl-2-styrylchromones in excellent yields. The low solubility of the target molecules allows convenient isolation. The formation of an α,α-dicinnamoylated acetophenone, as a consequence of a two-fold Baker-Venkataraman sequence, has to be anticipated.

Die “grüne” elektrochemische Synthese von Periodat

Diversitäts-orientierte Synthese von polycyclischen Gerüsten durch Umsetzung eines von 2,4-Dimethylphenol abgeleiteten anodischen Zwischenproduktes

Innenrücktitelbild: Metall- und reagensfreie dehydrierende formale Benzyl-Aryl-Kreuzkupplung durch anodische Aktivierung in 1,1,1,3,3,3-Hexafluorpropan-2-ol (Angew. Chem. 37/2018)

Thieme Chemistry Journals Awardees – Where Are They Now? Molybdenum(V)-Mediated Synthesis of Nonsymmetric Diaryl and Aryl Alkyl Chalcogenides

Oxidative chalcogenation reaction using molybdenum(V) reagents provides fast access to a wide range of nonsymmetric aryl sulfides and selenides. The established protocol is tolerated by a variety of labile functions, protecting groups, and aromatic heterocycles. In particular, when labile moieties are present, the use of molybdenum(V) reagents provides superior yields compared to other oxidants.

Metal-free electrochemical fluorodecarboxylation of aryloxyacetic acids to fluoromethyl aryl ethers

Electrochemical decarboxylation of aryloxyacetic acids followed by fluorination provides easy access to fluoromethyl aryl ethers. This electrochemical fluorodecarboxylation offers a sustainable approach with electric current as traceless oxidant. Using Et3N·5HF as fluoride source and as supporting electrolyte, this simple electrosynthesis affords various fluoromethoxyarenes in yields up to 85%.

Porous organic cage compounds as highly potent affinity materials for sensing by quartz crystal microbalances.

Porosity makes powerful affinity materials for quartz crystal microbalances. The shape-persistent organic cages and pores create superior affinity systems to existing ones for direct tracing of aromatic solvent vapors. A shape and size selectivity for the analytes is observed. These organic cages can be processed to thin films with highly reproducible sensing properties.

Advances in photochemical and electrochemical incorporation of sulfur dioxide for the synthesis of value-added compounds.

Organic photochemistry and electrochemistry currently receive tremendous attention in organic synthesis as both techniques enable the reagent-less activation of organic molecules without using expensive and hazardous redox reagents. The incorporation of SO2 into organic molecules is a relatively modern research topic, which likewise gains immense popularity since the discovery of the SO2 surrogate DABSO. Sulfur-containing organic molecules are omnipresent in pharmaceuticals and agrochemicals. This review covers the recent progress in electrochemical and photochemical methodologies for the incorporation and uses of SO2 in the synthesis of value-added compounds. Additionally, different work t…

ChemInform Abstract: (-)-Isosteviol as a Versatile Ex-Chiral-Pool Bulding Block for Organic Chemistry

Elektrifizierung der organischen Synthese

Sustainable electroorganic synthesis of lignin-derived dicarboxylic acids

The oxidative ring opening of lignin-derived alkylated cyclohexanols to bio-based alkylated dicarboxylic acids is successfully performed by an electrocatalytic conversion. To establish this transformation as a green method, we developed a simple protocol for the anodic oxidation at nickel oxide-hydroxide (NiOOH) foam anodes in caustic soda in both a batch and flow electrolysis approach.

Einfache und doppelte metall- und reagensfreie anodische C-C-Kreuzkupplung von Phenolen mit Thiophenen

Erstmals ist es gelungen, eine elektrochemische dehydrierende C-C-Kreuzkupplung von Thiophenen mit Phenolen durchzufuhren. Diese nachhaltige und einfache anodische Kreuzkupplung eroffnet den Zugang zu zwei besonders interessanten Substanzklassen. Das Anwendungsgebiet der C-H-aktivierenden elektrochemischen Kreuzkupplung wurde dabei um Schwefelheterocyclen erweitert. Bisher konnten nur verschiedene benzoide aromatische Systeme umgesetzt werden, wohingegen die Verwendung von Heterocyclen bei der C-H-aktivierenden elektrochemischen Kreuzkupplung nicht erfolgreich war. In diesem Fall bieten reagens- und metallfreie Bedingungen einen nachhaltigen elektrochemischen Weg und damit einen vielverspre…

Cover Picture: Diversity-Oriented Synthesis of Polycyclic Scaffolds by Modification of an Anodic Product Derived from 2,4-Dimethylphenol (Angew. Chem. Int. Ed. 6/2011)

Modular Approach to 9-Monosubstituted Fluorene Derivatives Using Mo(V) Reagents.

Oxidative coupling using molybdenum(V) reagents provides fast access to highly functionalized 9-monosubstituted fluorenes. This synthetic approach is highly modular, is high yielding, and tolerates a variety of labile moieties, e.g. amides or iodo groups. The established protocol leads to promising precursors for pharmacologically important analogues of melatonin.

Poly(2-vinylpyridine)-Based Polymers as an Efficient Affinity Material for the Detection of Airborne Phenol

Phenol is an omnipresent compound in various situations. Its acute toxicity makes alternative tracing methods desirable. Highly potent affinity materials based on polyvinyl pyridine allow an efficient tracing of this particular airborne compound. Their performance over, for example, benzene is tremendously superior. In combination with a simple cyclodextrin derivative an array allows differentiation among such aromatic competitors. Owing to the high affinity of these polymers for phenol, quartz microbalance-based tracing is able to detect phenol below the parts per million range. This was previously not possible with other affinity materials.

Efficient Resolution of Menthylamine with Inexpensive (R,R)-Tartaric Acid by Dielectrically Controlled Resolution (DCR)

A practical procedure for the resolution of menthylamine 2 with (R,R)-tartaric acid [(R,R)-3] as resolving agent is presented. Variation of the solvent system allows both enantiomers of 2 to be selectively crystallized. Performing the resolution in methanol containing 6 % water leads to (–)-2·(R,R)-3·MeOH. The other, less-soluble diastereomeric salt is obtained by applying a solvent system consisting of methanol with 19 % water with a yield of 14 %. Subsequent basic workup with aqueous sodium hydroxide gave the free menthylamine compounds. Further workup of the mother liquors and an additional recrystallization step allowed the (–)-2·(R,R)-3·MeOH salt to be obtained in an overall yield of 2…

Sustainable access to biobased biphenol epoxy resins by electrochemical dehydrogenative dimerization of eugenol

Limited fossil resources require innovative monomers and polymers derived from renewable feedstocks such as plant biomass. Thermosetting epoxy resins largely rely on petrochemical bisphenol-type monomers, which give high performance materials but are controversial due to their effects on human health. Herein, we present two biobased epoxy resins by direct dehydrogenative dimerization of eugenol, the main component of clove oil. Taking the Principles of Green Chemistry into account, we developed electrochemical dehydrodimerization at reticulated vitreous carbon (RVC) electrodes using methanol as environmentally benign solvent. Thus, fluorinated solvents such as 1,1,1,3,3,3-hexafluoroisopropa…

Dehydrierende anodische C‐C‐Kupplung von Phenolen mit elektronenziehenden Substituenten

Oxidative (Cross-)Coupling Reactions Mediated by C-H Activation of Thiophene Derivatives by Using Molybdenum(V) Reagents

Oxidative coupling by using molybdenum pentachloride provides fast and modular access to sophisticated thienoacenes in excellent yields. The coupling process can be accomplished with thiophene and benzothiophene derivatives and provides various complex skeletons such as spirocyclic compounds. In this approach, the first cross-coupling reactions with the use of MoCl5 were established and important motifs for semiconducting materials were synthesized.

Selektive Synthese teilgeschützter unsymmetrischer Biphenole durch reagens‐ und metallfreie anodische Kreuzkupplung

Titelbild: Diversitäts-orientierte Synthese von polycyclischen Gerüsten durch Umsetzung eines von 2,4-Dimethylphenol abgeleiteten anodischen Zwischenproduktes (Angew. Chem. 6/2011)

Cathodic Corrosion of Metal Electrodes—How to Prevent It in Electroorganic Synthesis

The critical aspects of the corrosion of metal electrodes in cathodic reductions are covered. We discuss the involved mechanisms including alloying with alkali metals, cathodic etching in aqueous and aprotic media, and formation of metal hydrides and organometallics. Successful approaches that have been implemented to suppress cathodic corrosion are reviewed. We present several examples from electroorganic synthesis where the clever use of alloys instead of soft neat heavy metals and the application of protective cationic additives have allowed to successfully exploit these materials as cathodes. Because of the high overpotential for the hydrogen evolution reaction, such cathodes can contri…

Potent affinity material for tracing acetone and related analytes based on molecular recognition by halogen bonds.

Affinity materials based on halogen bonds turned out to be a powerful tool for the molecular recognition of acetone or related carbonyl compounds in the presence of ubiquitous protic molecules. The superior selectivity and sensitivity were found by the gravimetric detection of volatile organic compounds by quartz crystal microbalances.

ChemInform Abstract: Efficient Anodic and Direct Phenol-Arene C,C Cross-Coupling: The Benign Role of Water or Methanol.

For the first time a significantly improved electrochemical C-C cross-coupling is reported.

(-)-Isosteviol as a Versatile Ex-Chiral-Pool Building Block for Organic Chemistry (Eur. J. Org. Chem. 25/2013)

Electrochemical nitration with nitrite

Aromatic nitration has tremendous importance in organic chemistry as nitroaromatic compounds serve as versatile building blocks. This study represents the electrochemical aromatic nitration with NBu4 NO2 , which serves a dual role as supporting electrolyte and as a safe, readily available, and easy-to-handle nitro source. Stoichiometric amounts of 1,1,1-3,3,3-hexafluoroisopropan-2-ol (HFIP) in MeCN significantly increase the yield by solvent control. The reaction mechanism is based on electrochemical oxidation of nitrite to NO2 , which initiates the nitration reaction in a divided electrolysis cell with inexpensive graphite electrodes. Overall, the reaction is demonstrated for 20 examples w…

Frontispiece: The “Green” Electrochemical Synthesis of Periodate

From Screening to Scale-Up: The DoE-Based Optimization of Electrochemical Reduction of l-Cystine at Metal Cathodes

Design of experiment (DoE) is a powerful statistical tool in establishing improved chemical processes. An optimization and scale-up of the electrochemical reduction of l-cystine to l-cysteine is pr...

ChemInform Abstract: Access to Pyrazolidin-3,5-diones Through Anodic N-N Bond Formation.

Pyrazolidin-3,5-diones are important motifs in heterocyclic chemistry and are of high interest for pharmaceutical applications. In classic organic synthesis, the hydrazinic moiety is installed through condensation using the corresponding hydrazine building blocks. However, most N,N'-diaryl hydrazines are toxic and require upstream preparation owing to their low commercial availability. We present an alternative and sustainable synthetic approach to pyrazolidin-3,5-diones that employs readily accessible dianilides as precursors, which are anodically converted to furnish the N-N bond. The electroconversion is conducted in a simple undivided cell under constant-current conditions.

Überoxidation als Schlüsselschritt im Mechanismus der MoCl5 - vermittelten dehydrierenden Arenkupplung

Oxidative Coupling Reactions of 1,3-Diarylpropene Derivatives to Dibenzo[a,c]cycloheptenes by PIFA

The oxidative cyclization reactions of a variety of α-benzyl-cinnamates can be selectively performed with hypervalent iodine as an oxidant. The dibenzo[a,c]cycloheptenes were isolated in up to 55 % yield. When an oxo substrate is applied, the yield was significantly increased. With this synthetic approach, a central intermediate for the synthesis of metasequirin-B was obtained in three steps from very simple starting materials. For this transformation, both aryl moieties have to be activated.

Metallfreie, elektrochemische Synthese von Sulfonamiden direkt aus (Hetero)arenen, SO 2 und Aminen

MoVReagents in Organic Synthesis

The use of MoV reagents, and in particular MoCl5, in organic synthesis is surveyed. The oxidative treatment of aromatic substrates is the most common application. The unique properties of these reagents are due to their high oxidative power combined with exquisite Lewis acid properties. In several examples MoV reagents outperform other common oxidative coupling reagents. C–C bond formation through inter- and intramolecular oxidative coupling can lead to selective formation of five- to eight-membered ring systems. Mechanistic investigations of the courses of reactions involving MoV reagents and aromatic substrates indicate that radical cations are initially formed, entering the oxidative cou…

Metal- and Reagent-Free Dehydrogenative Formal Benzyl-Aryl Cross-Coupling by Anodic Activation in 1,1,1,3,3,3-Hexafluoropropan-2-ol

A selective dehydrogenative electrochemical functionalization of benzylic positions that employs 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP) has been developed. The electrogenerated products are versatile intermediates for subsequent functionalizations as they act as masked benzylic cations that can be easily activated. Herein, we report a sustainable, scalable, and reagent- and metal-free dehydrogenative formal benzyl-aryl cross-coupling. Liberation of the benzylic cation was accomplished through the use of acid. Valuable diarylmethanes are accessible in the presence of aromatic nucleophiles. The direct application of electricity enables a safe and environmentally benign chemical transformati…

One-Pot Synthesis to Quinone-Based Diaza[3.3]cyclophanes

A simple one-pot synthesis to [3.3]cyclophanes that involves quinone moieties was found. The protocol tolerates a variety of amines that include aliphatic and aromatic structures with different functional groups, such as hydroxy groups, amides, and terminal double and triple bonds. The straightforward synthesis can be performed by a twofold N-alkylation reaction with 2,5-bis(bromomethyl)-3,6-dimethyl-1,4-benzoquinone (1). Neither anhydrous nor inert conditions are required. Various amines can be employed without any activating groups, several functionalities at end groups are tolerated, and the cyclophanes generated can be easily modified or embedded into larger molecular architectures. The…

Simple and scalable electrochemical synthesis of 2,1-benzisoxazoles and quinoline N-oxides.

Cathodic reduction of the nitro moiety and subsequent intramolecular cyclization affords different substituted 2,1-benzisoxazoles and quinoline N-oxides. This methodology allows the synthesis of two different types of heterocycles from common simple starting materials, using electrons as a sole reagent for this transformation. The electrolysis can be conducted in a very simple undivided electrolysis cell under constant current conditions. This permits working on a larger scale compared to other electrochemical methodologies and represents a significant advantage.

Straightforward Electrochemical Sulfonylation of Arenes and Aniline Derivatives using Sodium Sulfinates

Over-Oxidation as the Key Step in the Mechanism of the MoCl5-Mediated Dehydrogenative Coupling of Arenes.

Molybdenum pentachloride is an unusually powerful reagent for the dehydrogenative coupling of arenes. Owing to the high reaction rate using MoCl5, several labile moieties are tolerated in this transformation. The mechanistic course of the reaction was controversially discussed although indications for a single electron transfer as the initial step were found recently. Herein, based on a combined study including synthetic investigations, electrochemical measurements, EPR spectroscopy, DFT calculations, and mass spectrometry, we deduct a highly consistent mechanistic scenario: MoCl5 acts as a one-electron oxidant in the absence of TiCl4 and as two-electron oxidant in the presence of TiCl4, bu…

Highly selective generation of vanillin by anodic degradation of lignin: a combined approach of electrochemistry and product isolation by adsorption

The oxidative degradation of lignin into a variety of valuable products has been under investigation since the first half of the last century. Especially, the chance to claim this cheap, abundant and renewable source for the production of the important aroma chemical vanillin (1) was one of the major driving forces of lignin research. So far most of the developed methods fail in technical application since no viable concept for work-up is included. This work represents a combined approach of electrochemical conversion of Kraft lignin and product recovery by adsorption on a strongly basic anion exchange resin. Electrolysis conditions are optimized regarding reaction temperatures below 100 °C…

Luminescence dynamics of hybrid ZnO nanowire/CdSe quantum dot structures

Colloidal CdSe quantum dots (QDs) functionalized with different organic linker molecules are attached to ZnO nanowires (NWs) to investigate the electron transfer dynamics between dots and wires. After linking the quantum dots to the nanowires, the photo-induced electron transfer (PET) from the QDs into the NWs becomes visible in the PL transients by a decrease of dot luminescence decay time. The different recombination paths inside the QDs and the PET process are discussed in the framework of a rate equation model. Photoconductivity studies confirm the electron transfer by demonstrating a strong enhancement of the wire photocurrent under light irradiation into the dot transition. (© 2016 WI…

Electrochemical Screening for Electroorganic Synthesis

Electrochemical screening is usually strongly focused on electroanalytical data, while the parameters of organic synthesis are mostly not used as selection criteria. Typical parameters would be indication of the formation of the product and the efficiency of the electroorganic conversion. The latter data indicate the stability of the product under electrolysis conditions and represent the key for the accumulation of the desired product. We survey the current methods for electroorganic screening. In particular, parallel electrolysis under more defined conditions is discussed in detail since it represents a powerful tool for the development of electroorganic syntheses and processes.

Biobased Epoxy Resin by Electrochemical Modification of Tall Oil Fatty Acids

A biobased epoxy resin was prepared from tall oil fatty acids (TOFAs), a byproduct of the pulping industry. As free carboxylic acids compromise resin stability, TOFA was subjected to non-Kolbe decarboxylation to give alkenes upon loss of CO2. Thereby, the degree of unsaturation is significantly increased. This electrosynthetic protocol using an undivided cell setup and inexpensive graphite electrodes in a galvanostatic operation mode was scaled to a 1.5 L reactor, making use of electric current as a green and waste-free reagent. Simple, cost-efficient epoxidation using oxone subsequently gives an epoxy resin of low viscosity. Curing with anhydrides yields thermoset materials. Dynamic mechan…

Recent advances in the electrochemical reduction of substrates involving N−O Bonds

Scalable and Selective Preparation of 3,3′,5,5′-Tetramethyl-2,2′-biphenol

Biphenols are indispensable building blocks in ligand systems for organic catalysis. 3,3′5,5′-Tetramethyl-2,2′-biphenol is a particular versatile motif in different catalytic systems. We developed an easy to perform and scalable process to give access to large quantities of this important building block by the use of selenium dioxide, a common and readily available oxidizer.

Regioselektive metall‐ und reagenzfreie Arylierung von Benzothiophenen durch dehydrierende Elektrosynthese

Electrochemical Allylic Oxidation of Olefins: Sustainable and Safe.

The power you're supplying: With the application of an optimized electrochemical approach, the allylic oxidation of olefins, which is an important C-H activation process that provides access to enones, becomes a sustainable, versatile, and potent key reaction for organic synthesis.

Metal- and reagent-free highly selective anodic cross-coupling reaction of phenols.

The direct oxidative cross-coupling of phenols is a very challenging transformation, as homo-coupling is usually strongly preferred. Electrochemical methods circumvent the use of oxidizing reagents or metal catalysts and are therefore highly attractive. Employing electrolytes with a high capacity for hydrogen bonding, such as methanol with formic acid or 1,1,1,3,3,3-hexafluoro-2-propanol, a direct electrolysis in an undivided cell provides mixed 2,2′-biphenols with high selectivity. This mild method tolerates a variety of moieties, for example, tert-butyl groups, which are not compatible with other strong electrophilic media but vital for later catalytic applications of the formed products.

Synthesis of Optically Pure Arylamine Derivatives by Using the Bucherer Reaction

The Bucherer reaction is a common pathway for the conversion of 1- and 2-naphthols into the corresponding 1- or 2-naphthylamines, respectively. Mostly, only singular examples for its preparative use are reported since this particular transformation seems to be very sensitive to the reaction conditions. By choosing different phenolic substrates and chiral amines, we were able to prepare a broad scope of optically pure arylamines using this type of reaction. In contrast to alternative methods forming C−N aryl bonds such as Buchwald-Hartwig or Chan-Lam cross-coupling reactions, no palladium or copper catalysts are required. The use of water as solvent and the easily available starting material…

Shifting the Photoresponse of ZnO Nanowires into the Visible Spectral Range by Surface Functionalization with Tailor-Made Carbon Nanodots

We report on the surface functionalization of ZnO nanowires (NWs) with specifically synthesized carbon nanodots (C-dots, CDs) that allows us to shift the photoresponse of the NWs far into the visib...

Optimization Strategies for the Anodic Phenol‐Arene Cross‐Coupling Reaction

Electrochemistry of Carbon Dioxide on Carbon Electrodes.

Carbon electrodes have the advantages of being chemically inert at negative potential ranges in all media and high offset potentials for hydrogen evolution in comparison to metal electrodes, and therefore are the most suitable electrodes for electrochemistry and electrochemical conversion of CO2 into valuable chemicals. Herein we summarize on carbon electrodes the voltammetry, electrochemical and electrocatalytic CO2 reduction, as well as electron synthesis using CO2 and carbon electrodes. The electrocatalytic CO2 reduction using carbocatalyts and the future activities about electrochemical CO2 conversion are highlighted.

Metal- and Reagent-Free Electrochemical Synthesis of Alkyl Arylsulfonates in a Multi-Component Reaction.

Abstract This work presents the first electrochemical preparation of alkyl arylsulfonates by direct anodic oxidation of electron‐rich arenes. The reaction mechanism features a multi‐component reaction consisting of electron‐rich arenes, an alcohol of choice and excess SO2 in an acetonitrile‐HFIP reaction mixture. In‐situ formed monoalkyl sulfites are considered as key intermediates with bifunctional purpose. Firstly, this species functions as nucleophile and secondly, excellent conductivity is provided. Several primary and secondary alcohols and electron‐rich arenes are implemented in this reaction to form the alkyl arylsulfonates in yields up to 73 % with exquisite selectivity. Boron‐doped…

Large, Highly Modular Narrow-Gap Electrolytic Flow Cell and Application in Dehydrogenative Cross-Coupling of Phenols

The successive scale-up of electrochemical reactions is crucial with regard to the implementation of technical electro-organic syntheses. Therefore, we developed a scalable modular parallel-plate e...

Application of Rigidity-Controlled Supramolecular Affinity Materials for the Gravimetric Detection of Hazardous and Illicit Compounds.

The combination of an (-)-isosteviol-derived building block and 9,9'-spirobifluorene or tetraphenylmethane generated highly potent new affinity materials for the detection of volatile organic compounds (VOCs). Comparison of their affinity behaviour with different core structures showed remarkable influence on selectivity and sensitivity due to structural rigidity and their pre-organization. Their unique supramolecular properties were investigated in an affinity assay using high fundamental frequency quartz crystal microbalances.

(Organic and Biological Electrochemistry Division Manuel M. Baizer Award Address) Making Electroorganic Synthesis More Practical

The direct use of electrochemistry for the generation of reactive intermediates can have major advantages towards conventional synthetic strategies.[1] Less or no reagent waste is generated and new reaction pathways are accessible.[2] In order to exploit the electricity driven conversions for synthetic purposes and to install unique selectivity two modern approaches will be outlined: Solvent-controlled selective dehydrogenative cross-coupling reactions: A key for this is the use of boron-doped diamond anodes and fluorinated alcohols within the electrolyte.[3] This methodology opened new pathways for innovative and scalable arylation reactions.[4] New electrode systems for the anodic and ca…

Moderne Aspekte der Elektrochemie zur Synthese hochwertiger organischer Produkte

About the selectivity and reactivity of active nickel electrodes in C–C coupling reactions

Active anodes which are operating in highly stable protic media such as 1,1,1,3,3,3-hexafluoroisopropanol are rare. Nickel forms, within this unique solvent, a non-sacrificial active anode at constant current conditions, which is superior to the reported powerful molybdenum system. The reactivity for dehydrogenative coupling reactions of this novel active anode increases when the electrolyte is not stirred during electrolysis. Besides the aryl-aryl coupling, a dehydrogenative arylation reaction of benzylic nitriles was found while stirring the mixture providing quick access to synthetically useful building blocks.

Electrochemical Fluorocyclization of N-Allylcarboxamides to 2-Oxazolines by Hypervalent Iodine Mediator

A resource saving protocol for the synthesis of 5-fluoromethyl-2-oxazolines by using electrochemistry has been realized. Thereby, a hypervalent iodine species I(III) is generated by anodic oxidation in the presence of Et3N·5HF and mediates the cyclization of N-allylcarboxamide to 5-fluoromethyl-2-oxazoline. This method allows application to various substrates furnishing the 2-oxazolines with yields up to 68%. The protocol is easy to conduct under constant current conditions offering a sustainable alternative over conventional reagent-based pathways.

Direct Metal‐ and Reagent‐Free Sulfonylation of Phenols with Sodium Sulfinates by Electrosynthesis

A novel electrochemical strategy for the synthesis of aryl sulfones by direct sulfonylation of phenols with sodium sulfinates has been developed. The C,S-coupling products are of particular interest for chemical synthesis, material sciences and pharmaceutical sciences. By using this metal- and reagent-free electrochemical method, aryl and diaryl sulfones can be obtained directly in good yields. The established one-step protocol is easy to perform, scalable, inherently safe, and enables a broad scope, which is not limited by quinoid-forming substrates.

Twofold Electrochemical Amination of Naphthalene and Related Arenes

The twofold, electrochemical amination reaction of polycyclic arenes, e.g. naphthalene (4), via Zincke intermediates is demonstrated for the first time. The installation of the nitrogen functionalities occurs regioselectively in positions 1 and 5 of naphthalene (4). The key for this electro-conversion is boron-doped diamond as anode material. The method of the multi-amination reaction is expanded to other aromatic substrates. A detailed study is provided, covering electrolysis parameters, e.g. anode material, electrolyte system, current density, separator, etc. Despite the moderate yields, this approach offers the first direct electro-synthetic access to diaminated products.

ChemInform Abstract: Synthesis and Isolation of Enantiomerically Enriched Cyclopenta[b]benzofurans Based on Products from Anodic Oxidation of 2,4-Dimethylphenol.

Tetramer (I) is obtained by anodic oxidation of 2,4-dimethylphenol as reported in a previous paper.

Innentitelbild: Regioselektive metall‐ und reagenzfreie Arylierung von Benzothiophenen durch dehydrierende Elektrosynthese (Angew. Chem. 40/2018)

Total Synthesis of (-)-Oxycodone via Anodic Aryl-Aryl Coupling.

A fully regio- and diastereoselective electrochemical 4a–2′-coupling of a 3′,4′,5′-trioxygenated laudanosine derivative enables the synthesis of the corresponding morphinandienone. This key intermediate is further transformed into (−)-oxycodone through conjugate nucleophilic substitution for E-ring closure and [4 + 2] cycloaddition with photogenerated singlet oxygen to accomplish diastereoselective hydroxylation at C-14. The anodic transformation provides high yields and can be performed under constant current conditions both in a simple undivided cell or in continuous flow.

Novel Domino Oxidative Coupling: C−C Bond Formation Sequence to Highly Functionalized Dibenzo[a,c]cycloheptenes

A domino sequence involving various MoCl(5)-mediated oxidations followed by trapping and supposed [3,3]-sigmatropic rearrangement provides a fast access to the full carbon skeleton of metasequirin-B. A variety of different moieties R(1) and R(2) are tolerated.

Effiziente und stereodivergierende elektrochemische Synthese von optisch reinen Menthylaminen

Selective Formation of 4,4'-Biphenols by Anodic Dehydrogenative Cross- and Homo-Coupling Reaction.

A simple and selective electrochemical synthesis by dehydrogenative coupling of unprotected 2,6- or 2,5-substituted phenols to the desired 4,4'-biphenols is reported. Using electricity as the oxidizing reagent avoids pre-functionalization of the starting materials, since a selective activation of the substrates takes place. Without the necessity for metal-catalysts or the use of stoichiometric reagents it is an economic and environmentally friendly transformation. The elaborated electrochemical protocol leads to a broad variety of the desired 4,4'-biphenols in a very simplified manner compared to classical approaches. This is particular the case for the cross-coupled products.

Selective Synthesis of Partially Protected Nonsymmetric Biphenols by Reagent‐ and Metal‐Free Anodic Cross‐Coupling Reaction

The oxidative cross-coupling of aromatic substrates without the necessity of leaving groups or catalysts is described. The selective formation of partially protected nonsymmetric 2,2'-biphenols via electroorganic synthesis was accomplished with a high yield of isolated product. Since electric current is employed as the terminal oxidant, the reaction is reagent-free; no reagent waste is generated as only electrons are involved. The reaction is conducted in an undivided cell, and is suitable for scale-up and inherently safe. The implementation of O-silyl-protected phenols in this transformation results in both significantly enhanced yields and higher selectivity for the desired nonsymmetric 2…

Metal‐ and Reagent‐Free Anodic Dehydrogenative Cross‐Coupling of Naphthylamines with Phenols

ChemInform Abstract: Oxidative (Cross-)Coupling Reactions Mediated by C-H Activation of Thiophene Derivatives by Using Molybdenum(V) Reagents.

The use of MoCl5 renders possible the preparation of various synthetically important polycyclic thienoacenes.

Use of Diamond Films in Organic Electrosynthesis

Electroorganic synthesis of nitriles via a halogen-free domino oxidation–reduction sequence

A direct electroorganic sequence yielding nitriles from oximes in undivided cells is reported. Despite the fact that intermediate nitrile oxides might be formed, the method is viable to prepare benzonitriles without substituents ortho to the aldoxime moiety. This constant current method is easy to perform for a broad scope of substrates and employs common electrodes, such as graphite and lead.

Electrochemical synthesis of benzoxazoles from anilides - a new approach to employ amidyl radical intermediates.

A novel electrochemical method for the synthesis of benzoxazoles from readily available anilides is reported. Various functionalities are tolerated and good yields can be achieved. By employing common electrode materials and a simple constant current protocol, this method is an attractive new alternative to conventional pathways.

Frontispiz: Die “grüne” elektrochemische Synthese von Periodat

Adsorption and separation of black liquor-derived phenol derivatives using anion exchange resins

Abstract Kraft black liquor is the major waste stream of the paper pulping industry. This stream is usually directly incinerated in such facilities for energy production and recycling of the inorganic chemicals involved. However, lignin and other low molecular organic fragments dissolved in black liquor give rise to a large variety of aromatic fine chemicals. Energetic use of black liquor and its components prevents the removal of these valuable compounds from the waste stream. We present an easy protocol for adsorption and selective desorption of low molecular phenol derivatives from black liquor depending on the composition of the desorption system. Furthermore, adsorption experiments in …

Innentitelbild: Reagens- und metallfreie anodische C-C-Kreuzkupplung von Anilinderivaten (Angew. Chem. 17/2017)

Electrochemical Synthesis of Aryl Methoxymethyl Ethers

Systematic Investigation of Resorcin[4]arene-Based Cavitands as Affinity Materials on Quartz Crystal Microbalances.

Resorcin[4]arene cavitands are well-known supramolecular hosts, and their outstanding guest-binding abilities in solution have been studied in detail in recent decades. In a systematic approach, different resorcin[4]arene cavitands and container molecules are characterized as affinity materials for gravimetric sensing using high-fundamental-frequency quartz crystal microbalances. Analysis of their affinity toward a series of various analytes reveals a remarkable dependence of both selectivity and sensitivity on the shape, accessibility, and size of the cavity, along with their supramolecular interactions with the host molecules.

ChemInform Abstract: Solvent-Dependent Facile Synthesis of Diaryl Selenides and Biphenols Employing Selenium Dioxide.

The reaction of phenols (I) with selenium dioxide in pyridine leads to diaryl selenides (IIa-d), whilst the reaction in acetic acid gives rise to biphenols (III).

Interfacial Domain Formation Enhances Electrochemical Synthesis.

The electroorganic C,C coupling of phenols to other aryl components is controlled by the fluoroalcohol-alcohol mixture solvents. Classical molecular dynamics and static density functional theory reveal that both kinds of solvents interact with the substrates, influencing the electronic structure of a phenoxyl radical intermediate in a cooperative manner to achieve maximal efficiency and selectivity. Simulations of the electrolyte-electrode interface showed that the substrates adsorb on the diamond surface in such a way that the repulsive fluorous-lipophilic interactions can be minimized and the attractive lipophilic-lipophilic interplay can be maximized, whereas the advantageous hydrogen bo…

Frontispiece: A Novel Cathode Material for Cathodic Dehalogenation of 1,1‐Dibromo Cyclopropane Derivatives

Innentitelbild: Effiziente und stereodivergierende elektrochemische Synthese von optisch reinen Menthylaminen (Angew. Chem. 24/2011)

Frontispiece: Metal‐Free Electrochemical Synthesis of Sulfonamides Directly from (Hetero)arenes, SO 2 , and Amines

MoVReagents in Organic Synthesis (Eur. J. Org. Chem. 11/2016)

A Decade of Electrochemical Dehydrogenative C,C-Coupling of Aryls.

The importance of sustainable and green synthetic protocols for the synthesis of fine chemicals has rapidly increased during the last decades in an effort to reduce the use of fossil fuels and other finite resources. The replacement of common reagents by electricity provides a cost- and atom-efficient, environmentally friendly, and inherently safe access to novel synthetic routes. The selective formation of carbon-carbon bonds between two distinct substrates is a crucial tool in organic chemistry. This fundamental transformation enables access to a broad variety of complex molecular architectures. In particular, the aryl-aryl bond formation has high significance for the preparation of organ…

Electrical and photoelectrical measurements on ZnO-Nanowires coated with PEDOT:PSS for Dye-Sensitized Solar Cells

ABSTRACTDye-sensitized solar cells composed of an n-doped ZnO nanowire array and a p-doped polymer layer appears to be a promising candidate for low-cost production of environment-friendly solar cells. In this work, we investigate hybrid devices consisting of a transparent conducting oxide (TCO) substrate, ZnO-nanowires (ZnO-NW) or a sol-gel prepared ZnO layer, a ruthenium dye (N719) and a PEDOT:PSS or P3HT layer. The dense polycrystalline ZnO layer is able to prevent short circuits, which have a strong effect on the performance of the solar cells. This is demonstrated by the use of only the ZnO layer which improves the open circuit voltage by a factor of 2 and the efficiency by a factor of…

Influence of the Nature of Boron‐Doped Diamond Anodes on the Dehydrogenative Phenol‐Phenol Cross‐Coupling

Cover Picture: Source of Selectivity in Oxidative Cross-Coupling of Aryls by Solvent Effect of 1,1,1,3,3,3-Hexafluoropropan-2-ol (Chem. Eur. J. 35/2015)

Metal‐Free Twofold Electrochemical C−H Amination of Activated Arenes: Application to Medicinally Relevant Precursor Synthesis

Abstract The efficient production of many medicinally or synthetically important starting materials suffers from wasteful or toxic precursors for the synthesis. In particular, the aromatic non‐protected primary amine function represents a versatile synthetic precursor, but its synthesis typically requires toxic oxidizing agents and transition metal catalysts. The twofold electrochemical amination of activated benzene derivatives via Zincke intermediates provides an alternative sustainable strategy for the formation of new C−N bonds of high synthetic value. As a proof of concept, we use our approach to generate a benzoxazinone scaffold that gained attention as a starting structure against ca…

Stabilizing Lead Cathodes with Diammonium Salt Additives in the Deoxygenation of Aromatic Amides

Lead is efficiently protected against cathodic corrosion by the addition of diammonium salts in the electrolyte. The cationic coating of the cathode allows the efficient electroreduction of benzamides to benzylamines. The electrochemical deoxygenation of the amide is achieved without the use of oxophilic agents or sacrificial anodes. The surface of the lead cathode stays smooth and the cathode can be reused for multiple runs, providing <2.5 ppm of the crude product. Cyclic voltammetry studies reveal a shift in the onset potential of the hydrogen evolution reaction by −157 mV.

Inside Cover: Regioselective Metal‐ and Reagent‐Free Arylation of Benzothiophenes by Dehydrogenative Electrosynthesis (Angew. Chem. Int. Ed. 40/2018)

Electrochemical synthesis of carbazoles by dehydrogenative coupling reaction

Abstract A constant current protocol, employing undivided cells, a remarkably low supporting electrolyte concentration, inexpensive electrode materials, and a straightforward precursor synthesis enabling a novel access to N‐protected carbazoles by anodic N,C bond formation using directly generated amidyl radicals is reported. Scalability of the reaction is demonstrated and an easy deblocking of the benzoyl protecting group is presented.

Back Cover: A Regio- and Diastereoselective Anodic Aryl-Aryl Coupling in the Biomimetic Total Synthesis of (−)-Thebaine (Angew. Chem. Int. Ed. 34/2018)

Direct Anodic Dehydrogenative Cross- and Homo-Coupling of Formanilides

ChemInform Abstract: Modular Approach to 9-Monosubstituted Fluorene Derivatives Using MoVReagents.

Optical Sensor for Real-Time Detection of Trichlorofluoromethane

Trichlorofluoromethane was once a promising and versatile applicable chlorofluorocarbon. Unaware of its ozone-depleting character, for a long time it was globally applied as propellant and refrigerant and thus led to significant thinning of the ozone layer and contributed to the formation of the so-called ozone hole. Although production and application of this substance were gradually reduced at an early stage, we still face the consequences of its former careless use. Today, trichlorofluoromethane is released during recycling processes of waste cooling devices, traded on the black market, and according to recent findings still illegally manufactured. Here, we present an optical sensor devi…

Electro-conversion as sustainable method for the fine chemical production from the biopolymer lignin

Lignin, one of the most abundant polymers in nature, qualifies itself by the polyphenolic structure as potential renewable feedstock for the production of bio-based aromatic fine chemicals. However, the natural complexity and degradation stability of lignin make the depolymerization a highly challenging task. Several efforts have been pursued for the selective degradation of the biopolymer into suitable compounds. However, there are only a few technical approaches for the degradation of lignin to aromatic fine chemicals. Organic electrosynthesis is the synthetic method that enables the direct use of electricity for the production of valuable compounds. Moreover, electro-organic synthesis re…

Efficient and stereodivergent electrochemical synthesis of optically pure menthylamines.

Modular Access to 9,9-Spirobifluorenes by Oxidative Coupling Using Molybdenum Pentachloride

The strong oxidizing agent molybdenum pentachloride was used for an efficient direct C–C bond formation of 9,9-diarylfluorenes to the corresponding 9,9-spirobifluorenes. Thus, a versatile method that is compatible with labile groups, such as iodo moieties, was established. By this approach important building blocks for light emitting polymers were synthesized in high yields.

Electrochemical Amination of Less-Activated Alkylated Arenes Using Boron-Doped Diamond Anodes

The anodic C–H amination of aromatic compounds is a powerful and versatile method for the synthesis of aniline derivatives. By using boron-doped diamond (BDD) anodes, a method initially described by Yoshida et al. for electron-rich arenes was expanded to less-activated aromatic systems e.g., simple alkylated benzene derivatives. Anodes based on sp3 carbon seem to be the key for the electrochemical amination reaction. The corresponding primary anilines are obtained in good yields. Despite the cationic intermediates of the electrolytic reaction tert-butyl moieties are tolerated.

ChemInform Abstract: Synthesis of meta-Terphenyl-2,2′′-diols by Anodic C-C Cross-Coupling Reactions.

The anodic C−C cross-coupling reaction is a versatile synthetic approach to symmetric and non-symmetric biphenols and arylated phenols. We herein present a metal-free electrosynthetic method that provides access to symmetric and non-symmetric meta-terphenyl-2,2′′-diols in good yields and high selectivity. Symmetric derivatives can be obtained by direct electrolysis in an undivided cell. The synthesis of non-symmetric meta-terphenyl-2,2′′-diols required two electrochemical steps. The reactions are easy to conduct and scalable. The method also features a broad substrate scope, and a large variety of functional groups are tolerated. The target molecules may serve as [OCO]3− pincer ligands.

Optical planar Bragg grating sensor for real-time detection of benzene, toluene and xylene in solvent vapour

Abstract We report on an optical planar Bragg grating sensor functionalized by a comparatively simple method to detect substances such as benzene, toluene and xylene (BTX). The functionalization is performed by allyl substituted γ -cyclodextrin derivatives which are immobilized on the sensor surface by dip coating. Our results prove the capability of this functionalized sensor system to detect lowest concentrations of BTX in solvent vapour in real-time with a sensitivity of 3±0.4 pm/100 ppm for benzene, 8±1 pm/100 ppm for toluene and 32±1 pm/100 ppm for m-xylene. Taking into account the spectral resolution and repeatability of the interrogation system this corresponds to a minimum concentra…

Source of Selectivity in Oxidative Cross-Coupling of Aryls by Solvent Effect of 1,1,1,3,3,3-Hexafluoropropan-2-ol

Abstract Solvents such as 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) with a high capacity for donating hydrogen bonds generate solvates that enter into selective cross-coupling reactions of aryls upon oxidation. When electric current is employed for oxidation, reagent effects can be excluded and a decoupling of nucleophilicity from oxidation potential can be achieved. The addition of water or methanol to the electrolyte allows a shift of oxidation potentials in a specific range, creating suitable systems for selective anodic cross-coupling reactions. The shift in the redox potentials depends on the substitution pattern of the substrate employed. The concept has been expanded from arene-phenol…

Oxidative transformation of aryls using molybdenum pentachloride.

Molybdenum pentachloride combines a strong Lewis acid character with an unusually high oxidation potential creating a powerful reagent for oxidative transformations. Since the oxidative coupling reaction of aryls is induced at an extraordinarily high reaction rate, a variety of labile groups, e.g. iodo, tert-alkyl, etc., are tolerated on the aromatic core. Furthermore, the co-formed molybdenum salts can either be exploited for template effects to obtain uncommon geometries in a preferred manner, or redox-play starts after aqueous workup. Therefore MoCl(5) represents a unique and easily available reagent.

Anodische dehydrierende Cyaniminierung von Thioethern: eine einfache und nachhaltige Synthese von N ‐Cyansulfiliminen

The “green” electrochemical synthesis of periodate

Abstract High‐grade periodate is relatively expensive, but is required for many sensitive applications such as the synthesis of active pharmaceutical ingredients. These high costs originate from using lead dioxide anodes in contemporary electrochemical methods and from expensive starting materials. A direct and cost‐efficient electrochemical synthesis of periodate from iodide, which is less costly and relies on a readily available starting material, is reported. The oxidation is conducted at boron‐doped diamond anodes, which are durable, metal‐free, and nontoxic. The avoidance of lead dioxide ultimately lowers the cost of purification and quality assurance. The electrolytic process was opti…

Highly Fluorinated 2,2′-Biphenols and Related Compounds: Relationship between Substitution Pattern and Herbicidal Activity

A broad range of halogenated 2,2'-biphenols was tested for applicability as crop protection agents. The activity of these compounds toward four typical pest plants was observed after application by spraying of diluted solutions. Despite their rather simple structure, it was found that the studied compounds reveal a surprisingly high herbicidal impact. To gain a better understanding of the structure-activity relationship, specific sites of the molecule were chemically modified and the core structures thus gradually changed. The influence of the substitution pattern on the herbicidal properties is discussed, and conclusions on the active site of the biphenol structure are drawn. It was observ…

Front Cover: Selective and Scalable Electrosynthesis of 2H ‐2‐(Aryl)‐benzo[ d ]‐1,2,3‐triazoles and Their N‐Oxides by Using Leaded Bronze Cathodes (Chem. Eur. J. 25/2020)

New Approach to 1,4-Benzoxazin-3-ones by Electrochemical C-H Amination.

1,4-Benzoxazin-3-ones are important structural motifs in natural products and bioactive compounds. Usually the synthesis of benzoxazinones requires transition metal catalysts and pre-functionalized substrates, e.g. aryl halides. However, the anodic C,H amination of phenoxy acetates offers a very efficient and sustainable access to these heterocycles. The herein presented electrochemical protocol can be applied to a broad scope of alkylated substrates. Even tert-butyl moieties or halogen substituents are compatible with this versatile method.

Development of a Method for Anodic Degradation of Lignin for the Analysis of Paleo‐Vegetation Proxies in Speleothems

ChemInform Abstract: Source of Selectivity in Oxidative Cross-Coupling of Aryls by Solvent Effect of 1,1,1,3,3,3-Hexafluoropropan-2-ol.

Abstract Solvents such as 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) with a high capacity for donating hydrogen bonds generate solvates that enter into selective cross-coupling reactions of aryls upon oxidation. When electric current is employed for oxidation, reagent effects can be excluded and a decoupling of nucleophilicity from oxidation potential can be achieved. The addition of water or methanol to the electrolyte allows a shift of oxidation potentials in a specific range, creating suitable systems for selective anodic cross-coupling reactions. The shift in the redox potentials depends on the substitution pattern of the substrate employed. The concept has been expanded from arene-phenol…

Investigations on isomerization and rearrangement of polycyclic arenes under oxidative conditions – Anodic versus reagent-mediated reactions

Abstract Electro-organic conversions at an active molybdenum anode enable the formation of fused arenes. High chemoselectivity was achieved under anodic conditions, and a reagent-induced selectivity was observed by comparison with results of MoCl5-mediated reactions. Polycyclic arenes like phenanthrenes, triphenylenes, chrysenes, or helicenes were selectively obtained in yields up to 87% and in some cases unusual rearrangements were crucial for the product formation.

Pollutant Adsorbtion and Detection: Methyl-Substituted α-Cyclodextrin as Affinity Material for Storage, Separation, and Detection of Trichlorofluoromethane (Global Challenges 8/2018)

The cover image depicts the hazard caused by chlorofluorocarbons such as CFC‐11, which are used, for example, as blowing agents for polyurethane foams, and the protective effect of the oligosaccharide, hexakis‐(2,3,6‐tri‐O‐methyl)‐α‐cyclodextrin, which is capable of binding CFC‐11 by supramolecular complexation and thus protecting the stratospheric ozone layer from the harmful trichlorofluoromethane. Further details can be found in article number 1800057 by Ralf Hellmann, Siegfried R. Waldvogel, and co‐workers.

Metall- und reagensfreie dehydrierende formale Benzyl-Aryl-Kreuzkupplung durch anodische Aktivierung in 1,1,1,3,3,3-Hexafluorpropan-2-ol

Boron-Doped Diamond Electrodes for Electroorganic Chemistry

Boron-doped diamond (BDD) electrodes provide an unusually wide electrochemical window in protic media, since there exist large offset potentials for the evolution of molecular hydrogen and oxygen, respectively. At the anode, alcohols are specifically converted to alkoxyl radicals. These can be used for chemical synthesis. When the enormous reactivity of such intermediate spin centers is not controlled, mineralization or electrochemical incineration dominates. Efficient strategies include either high substrate concentrations or fluorinated alcohols which seem to stabilize the spin centers in the course of reaction.

Fundamentals and Applications of Organic Electrochemistry. Synthesis, Materials, Devices. By Toshio Fuchigami, Mahito Atobe and Shinsuke Inagi.

Electro-organic synthesis – a 21st century technique

The severe limitations of fossil fuels and finite resources influence the scientific community to reconsider chemical synthesis and establish sustainable techniques. Several promising methods have emerged, and electro-organic conversion has attracted particular attention from international academia and industry as an environmentally benign and cost-effective technique. The easy application, precise control, and safe conversion of substrates with intermediates only accessible by this method reveal novel pathways in synthetic organic chemistry. The popularity of electricity as a reagent is accompanied by the feasible conversion of bio-based feedstocks to limit the carbon footprint. Several mi…

Bis(2,2'-biphenoxy)borates for electrochemical double-layer capacitor electrolytes.

Fluorine makes the difference! Bis(2,2'-biphenoxy)borates decorated with fluorine substituents have been synthesized and studied in supercapacitor test cells (see scheme). A clear trend towards higher electrochemical stability with the increase of the fluorine content has been observed. For a maximum performance, only two fluorine substituents per benzene moiety are required.

Cover Picture: Scaffold-Optimized Dendrimers for the Detection of the Triacetone Triperoxide Explosive Using Quartz Crystal Microbalances (ChemPlusChem 2/2012)

Synthesis ofmeta-Terphenyl-2,2′′-diols by Anodic C−C Cross-Coupling Reactions

The anodic C-C cross-coupling reaction is a versatile synthetic approach to symmetric and non-symmetric biphenols and arylated phenols. We herein present a metal-free electrosynthetic method that provides access to symmetric and non-symmetric meta-terphenyl-2,2''-diols in good yields and high selectivity. Symmetric derivatives can be obtained by direct electrolysis in an undivided cell. The synthesis of non-symmetric meta-terphenyl-2,2''-diols required two electrochemical steps. The reactions are easy to conduct and scalable. The method also features a broad substrate scope, and a large variety of functional groups are tolerated. The target molecules may serve as [OCO](3-) pincer ligands.

Mass‐Spectrometric Imaging of Electrode Surfaces—a View on Electrochemical Side Reactions

Abstract Electrochemical side reactions, often referred to as “electrode fouling”, are known to be a major challenge in electro‐organic synthesis and the functionality of modern batteries. Often, polymerization of one or more components is observed. When reaching their limit of solubility, those polymers tend to adsorb on the surface of the electrode, resulting in a passivation of the respective electrode area, which may impact electrochemical performance. Here, matrix‐assisted laser‐desorption/ionization mass spectrometry (MALDI‐MS) is presented as valuable imaging technique to visualize polymer deposition on electrode surfaces. Oligomer size distribution and its dependency on the contact …

Oxidative cyclization reaction of 2-aryl-substituted cinnamates to form phenanthrene carboxylates by using MoCl5.

The oxidative cyclization reaction of 2-aryl cinnamates and derivatives thereof can be easily performed with MoCl5 as the oxidant. This powerful reagent allows oxidative coupling reactions for which other reagents fail. The best results are obtained when the 2-phenyl substituent of the cinnamate is equipped with two methoxy groups. Even iodo moieties in the bay region of phenanthrene are tolerated under the reaction conditions. If naphthalene moieties are involved, a rearrangement of the skeleton occurs, providing an elegant route to highly functionalized angular arenes. The cyclization is demonstrated for 15 example substrates with isolated yields of up to 99 % for the phenanthrene derivat…

A New Reference Material and Safe Sampling of Terrorists Peroxide Explosives by a Non-Volatile Matrix

Synthesis of all-syn Functionalized Triphenylene Ketals

The stereoselective synthesis of triphenylene ketals offers access to unique scaffolds. For a good performance in supramolecular applications an all-syn orientation of the functional groups is essential. The oxidative trimerization of catechol ketals by molybdenum pentachloride or mixtures with titanium tetrachloride leads to a template-directed formation. Several heterocyclic moieties are suitable for this transformation. A template-directed isomerization of anti,anti,syn isomers to the desired C 3 -symmetric derivative was demonstrated in two cases.

Inside Cover: Reagent- and Metal-Free Anodic C−C Cross-Coupling of Aniline Derivatives (Angew. Chem. Int. Ed. 17/2017)

Vielfältige elektrochemische C-H-Aminierung über Zincke-Zwischenstufen

Electro-organic Synthesis as a Sustainable Alternative for Dehydrogenative Cross-Coupling of Phenols and Naphthols

The dehydrogenative cross-coupling of phenols and naphthols can be achieved by several oxidative methods. However, the key is the use of fluorinated alcohols such as 1,1,1,3,3,3-hexafluoroisopropanol. The direct application of electricity represents an alternative synthetic approach, which is superior to other oxidizers (e.g., peroxides). The method is sustainable, inherently safe, and easily scalable.

Mild, Fast, and Easy To Conduct MoCl5-Mediated Dehydrogenative Coupling Reactions in Flow

A convenient and straightforward approach to performing oxidative coupling reactions in flow is presented. A collection of electron-rich benzene derivatives was subjected to this protocol, and the distinct utility of molybdenum pentachloride (MoCl5) is established. Using this unexplored protocol, biphenyls could be obtained in 21–91% isolated yield. This simple protocol opens a new chapter in reagent-mediated dehydrogenative coupling reactions, and yields are compared to classical approaches.

Exploration of the Solid-State Sorption Properties of Shape-Persistent Macrocyclic Nanocarbons as Bulk Materials and Small Aggregates.

Porous molecular materials combine benefits such as convenient processability and the possibility for atom-precise structural fine-tuning which makes them remarkable candidates for specialty applications in the areas of gas separation, catalysis, and sensing. In order to realize the full potential of these materials and guide future molecular design, knowledge of the transition from molecular properties into materials behavior is essential. In this work, the class of compounds termed cycloparaphenylenes (CPPs)-shape-persistent macrocycles with built-in cavities and radially oriented π-systems-was selected as a conceptually simple class of intrinsically porous nanocarbons to serve as a platf…

Cover Feature: Electrochemical Installation of CFH 2 −, CF 2 H−, CF 3 −, and Perfluoroalkyl Groups into Small Organic Molecules (Chem. Rec. 9/2021)

ChemInform Abstract: Renaissance of Electrosynthetic Methods for the Construction of Complex Molecules

Current affairs: Efficient N,N dimerization by using an electric current is a recent powerful example of preparative electrosynthesis where conventional reagents fail. The general and practical nature of this method as well as other applications will breathe new life into the electroorganic synthesis of complex molecules.

Anodic coupling of guaiacol derivatives on boron-doped diamond electrodes.

The anodic treatment of guaiacol derivatives on boron-doped diamond electrodes (BDD) provides a direct access to nonsymmetrical biphenols, which would require a multistep sequence by conventional methods. Despite the destructive nature of BDD anodes they can be exploited for chemical synthesis.

Novel cuprous oxide morphologies using amino acids and carboxylic acids as structure directing agents in a simple hydrothermal method

Abstract The reactivity and catalytic performance of cuprous oxide (Cu2O) particles rely on the size and morphology of the Cu2O crystals. In this study, a facile and mild hydrothermal route is applied to generate novel uniform cuprous oxide microcrystals, using non-toxic and low-cost carboxylic acids (O,O-type) and amino acids (N,O-type) as structure directing agents. N,O-type complexing agents showed a higher ability to reduce the copper species compared to the O,O-type ligands. Using oxalate and citrate complexes, pure Cu2O was obtained after 4 h at 200 °C, whereas the oxalate-based complex leads to the morphology of uniformly stepped microcubes, the citrate complex as precursor leads to …

Reproduzierbarkeit in der elektroorganischen Synthese – Mythen und Missverständnisse

Anodic Dehydrogenative Cyanamidation of Thioethers: Simple and Sustainable Synthesis of N‐Cyanosulfilimines

Abstract A novel and very simple to perform electrochemical approach for the synthesis of several N‐cyanosulfilimines in good to excellent yields was established. This method provides access to biologically relevant sulfoximines by consecutive oxidation using electro‐generated periodate. This route can be easily scaled‐up to gram quantities. The S,N coupling is carried out at an inexpensive carbon anode by direct oxidation of sulfide. Therefore, the designed process is atom economic and represents a new “green route” for the synthesis of sulfilimines and sulfoximines.

Charged Tags for the Identification of Oxidative Drug Metabolites Based on Electrochemistry and Mass Spectrometry

Abstract Most of the active pharmaceutical ingredients like Metoprolol are oxidatively metabolized by liver enzymes, such as Cytochrome P450 monooxygenases into oxygenates and therefore hydrophilic products. It is of utmost importance to identify the metabolites and to gain knowledge on their toxic impacts. By using electrochemistry, it is possible to mimic enzymatic transformations and to identify metabolic hot spots. By introducing charged‐tags into the intermediate, it is possible to detect and isolate metabolic products. The identification and synthesis of initially oxidized metabolites are important to understand possible toxic activities. The gained knowledge about the metabolism will…

Functionalization of Silver Nanowires Surface using Ag–C Bonds in a Sequential Reductive Method

Silver nanowires (Ag-NW) assembled in interdigitated webs have shown an applicative potential as transparent and conducting electrodes. However, upon integration in practical device designs, the presence of silver oxide, which instantaneously forms on the Ag-NW surfaces in ambient conditions, is unwanted. Here, we report on the functionalization of Ag-NWs with 4-nitrophenyl moieties through A-C bonds using a versatile two step reduction process, i.e., ascorbate reduction combined electrografting. We show that 40% of the Ag atop sites were terminated and provide high surface stability toward oxidation for more than 2 months while keeping the same intrinsic conductivity as in bulk silver.

Electrochemical instability of highly fluorinated tetraphenyl borates and syntheses of their respective biphenyls

Highly fluorinated tetraphenyl borate anions are of importance as weakly coordinating anions in metalorganic reactions. However, at high positive potentials their electrochemical stability in organic solvents is not sufficient. This was investigated by a comprehensive cyclic voltammetry study and can be used synthetically to generate highly fluorinated biphenyls.

Synthesis of iodobiaryls and dibenzofurans by direct coupling at BDD anodes.

The first direct oxidative phenol-arene cross-coupling reactions of an iodine-containing guaiacol derivative and the possible over-oxidation products of electron-rich phenols are described. Hereby, a "green" and targeted synthesis for dibenzofurans was developed.

Electrochemical C−H Functionalization of (Hetero)Arenes—Optimized by DoE

Abstract A novel approach towards the activation of different arenes and purines including caffeine and theophylline is presented. The simple, safe and scalable electrochemical synthesis of 1,1,1,3,3,3‐hexafluoroisopropanol (HFIP) aryl ethers was conducted using an easy electrolysis setup with boron‐doped diamond (BDD) electrodes. Good yields up to 59 % were achieved. Triethylamine was used as a base as it forms a highly conductive media with HFIP, making additional supporting electrolytes superfluous. The synthesis was optimized using Design of Experiment (DoE) techniques giving a detailed insight to the significance of the reaction parameters. The mechanism was investigated by cyclic volt…

Outstandingly robust anodic dehydrogenative aniline coupling reaction

Abstract Oxidative treatment of anilines usually leads to the formation of black polymers, often referred to as “aniline black”. This over-oxidation is hardly controllable and also a challenging task in the anodic conversion of anilines. Here, a quick and efficient access to valuable building blocks by anodic cross- and homo-coupling of aniline and benzidine derivatives is reported. This electrosynthesis is easily performed in a simple undivided cell using constant current conditions. The key to the observed outstanding performance and robustness of this system is attributed to the used solvent 1,1,1,3,3,3-hexafluoroisopropanol. The extraordinary performance over a broad range of current de…

Toward Three-Dimensional Chemical Imaging of Ternary Cu–Sn–Pb Alloys Using Femtosecond Laser Ablation/Ionization Mass Spectrometry

Femtosecond laser ablation/ionization mass spectrometry (LIMS) has been applied to probe the spatial element composition of three ternary Cu-Sn-Pb model bronze alloys (lead bronzes: CuSn10Pb10, CuSn7Pb15, and CuSn5Pb20), which were recently identified as high-performance cathode materials in the context of electro-organic synthesis (dehalogenation, deoxygenation) of pharmaceutically relevant building blocks. The quantitative and spatially resolved element analysis of such cathode materials will help in understanding the observed profound differences in their electrochemical reactivity and stability. For that purpose, we developed a measurement procedure using the LIMS technique which allows…

Efficient Anodic and Direct Phenol-Arene C,C Cross-Coupling: The Benign Role of Water or Methanol

C,C cross-coupling reactions for the synthesis of nonsymmetrical biaryls represent one of the most significant transformations in contemporary organic chemistry. A variety of useful synthetic methods have been developed in recent decades, since nonsymmetrical biaryls play an evident role in natural product synthesis, as ligand systems in homogeneous catalysis and materials science. Transformation of simple arenes by direct C,H activation belongs to the cutting-edge strategies for creating biaryls; in particular the 2-fold C,H activation is of significant interest. However, in most examples very costly noble metal catalysts, ligand systems, and significant amount of waste-producing oxidants …

ChemInform Abstract: Electrochemical Amination of Less-Activated Alkylated Arenes Using Boron-Doped Diamond Anodes.

Eine regio- und diastereoselektive anodische Aryl-Aryl-Kupplung in der biomimetischen Totalsynthese von (−)-Thebain

3,4′,5,5′-Tetramethoxy-2′-methylbiphenyl-4-ol

The asymmetric unit of the title compound, C17H20O5, contains two independent molecules, A and B, with similar geometries [dihedral angles between the phenyl rings = 56.19 (8) and 54.98 (7)°, respectively]. Intramolecular O—H...O hydrogen bonds occur in both molecules. In the crystal, the A molecules form [1\overline{1}0] chains linked by O—H...O hydrogen bonds from the hydroxyl group to one of the methoxy O atoms. The B molecules form O—H...O hydrogen bonds to the hydroxyl O atoms of the A molecules and thus act as fixed spacers between the chains of molecule A. Some weak C—H...O contacts are also present.

Allylated cyclodextrins as effective affinity materials in chemical sensing of volatile aromatic hydrocarbons using an optical planar Bragg grating sensor

We report on the application of perallyl-substituted α-, β- and γ-cyclodextrins to an optical planar Bragg grating refractive index sensor for the effective sensitization of the sensor for airborne volatile aromatic hydrocarbons. Thereby, the emphasis of this work lies on the comparison of the different cyclodextrin types regarding their suitability as affinity material assessed by the sensors sensitivity and response behavior. The opto-chemical sensor device showed an immediate and quick response to the application of the investigated analytes benzene, toluene and m-xylene as well as a linear dependence on the concentration of those analytes. Studies on the sensors sensitivity depending on…

Electron tunneling from colloidal CdSe quantum dots to ZnO nanowires studied by time-resolved luminescence and photoconductivity experiments

CdSe quantum dots (QDs) with different organic linker molecules are attached to ZnO nanowires (NWs) to study the luminescence dynamics and the electron tunneling from the QDs to the nanowires in time-resolved photoluminescence (PL) and photoconductivity measurements. The PL transients of the QD luminescence indicate two different recombination channels: the direct recombination inside the QD core and the recombination via QD surface defect states. After linking the QDs to the ZnO NW surface, photo-induced electron tunneling from an excited state of the QD into the conduction band of the nanowire becomes visible by a clear decrease of the PL decay time. Efficient electron tunneling is confir…

Derivatives of (-)-Isosteviol with Expanded Ring D and Various Oxygen Functionalities

(–)-Isosteviol is a unique ex-chiral-pool building block that is readily available. Both functional groups are aligned in a concave manner. The methyl moiety on the backbone also points in this direction, creating a strong asymmetric environment close to these functional groups. The slightly divergent orientation of the keto and carboxy functions limits its use in the construction of supramolecular architectures as optically pure divalent building blocks. By selective transformations, ring D of (–)-isosteviol can be expanded and equipped with oxygen-containing functionalities, providing a variety of useful and rigid building blocks with defined stereochemistry.

Methyl-Substituted α-Cyclodextrin as Affinity Material for Storage, Separation, and Detection of Trichlorofluoromethane

Abstract The severely ozone‐depleting trichlorofluoromethane is still appearing in several recycling processes or industrial applications. A simple and selective supramolecular complex formation of per‐methylated α‐cyclodextrin (1) with the highly volatile trichlorofluoromethane (2) is reported. This interaction moreover leads to thermally stable crystals. Per‐methylated α‐cyclodextrin is successfully exploited as a reversible and selective adsorption material for liquid and airborne trichlorofluoromethane as well as an affinity material for the chemical sensing and detection of this particular volatile organic component.

Synthese vonmeta-Terphenyl-2,2′′-diolen durch anodische C-C-Kreuzkupplungen

Die anodische C-C-Kreuzkupplung ist eine vielseitig einsetzbare Transformation, die eine gezielte Synthese von Biphenolen und arylierten Phenolen ermoglicht. Wir berichten uber einen ebenfalls elektrosynthetischen, metallfreien Ansatz, der einen Zugang zu symmetrischen und nichtsymmetrischen meta-Terphenyl-2,2′′-diolen in guten Ausbeuten und hoher Selektivitat ermoglicht. Symmetrische Derivate konnen durch eine direkte Synthese in einer ungeteilten Zelle gewonnen werden, wohingegen nichtsymmetrische meta-Terphenyl-2,2′′-diole zwei elektrochemische Stufen benotigen. Die milde Methode ist einfach durchzufuhren und skalierbar. Auserdem konnte erstmalig eine breite Substratvariabilitat aufgezei…

Comprehensive valorisation of technically relevant organosolv lignins via anodic oxidation

Lignin represents the largest renewable feedstock of aromatic moieties in nature. However, its valorisation towards organic chemicals poses a challenging task. We herein report the selective electrochemical depolymerisation of several technically relevant organosolv lignins to aromatic fine chemicals with a simple two-electrode arrangement using caustic soda as electrolyte. Vanillin, syringaldehyde, the corresponding ketones and guaiacol were obtained with a combined maximum of 7.8 wt% isolated yield. Deeper insight in the process was provided by FT-IR, HSQC NMR and 31P NMR analyses of the lignins.

The Catalytic Effect of Fluoroalcohol Mixtures Depends on Domain Formation

In the present contribution, we investigated catalytically active mixtures of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and aqueous H2O2 by molecular dynamics simulations. It is clearly observable that the HFIP molecule strongly binds to the H2O2, which is necessary for the desired catalytic reaction to occur. Upon the addition of the substrate cyclooctene to the solution, this interaction is enhanced, which suggests that the catalytic activity is increased by the presence of the hydrocarbon. We could clearly observe the microheterogeneous structure of the mixture, which is the result of the separation of the hydroxyl groups, water, and H2O2 from the fluorinated alkyl moiety in the form of l…

Inside Back Cover: Metal- and Reagent-Free Dehydrogenative Formal Benzyl-Aryl Cross-Coupling by Anodic Activation in 1,1,1,3,3,3-Hexafluoropropan-2-ol (Angew. Chem. Int. Ed. 37/2018)

Total Synthesis of (±)-Oxalicumone C and Chiral Resolution and Elucidation of Its Absolute Configuration

The racemic total synthesis, the chiral resolution, and the elucidation of the absolute configuration of the natural product oxalicumone C were investigated. The goal was achieved by a synthetic strategy beginning with the synthesis of a 5-hydroxy-7-methylchromone precursor. Further modification possibilities were achieved by introduction of a vinyl moiety into the chromone, which was based on a selective iodination step in the 3-position. Further transformations furnished the racemic natural product. To determinate the absolute configuration of naturally occurring oxalicumone C, both enantiomers were separated by chiral HPLC. Comparison of the calculated and experimental vibrational circul…

Electrochemical Synthesis of Fluorinated Orthoesters from 1,3‐Benzodioxoles

Abstract Invited for this month's cover picture is the group of Professor Siegfried Waldvogel. The cover picture displays the robustness achieved by the installation of fluorinated alcohols on 1,3‐benzodioxoles, protecting the obtained orthoesters against acids and bases, like the shield of a knight. The simple protocol allows access to interesting compounds, whose lipophilicity is tremendously increased by the incorporation of fluorinated groups. This makes it possible to adjust the physicochemical properties of the biologically active 1,3‐benzodioxole motif. The surprisingly high stability against acids and bases gives rise to subsequent functionalizations or direct application in medicin…

Leaded Bronze Alloy as a Catalyst for the Electroreduction of CO 2

Reproducibility in Electroorganic Synthesis—Myths and Misunderstandings

Abstract The use of electric current as a traceless activator and reagent is experiencing a renaissance. This sustainable synthetic method is evolving into a hot topic in contemporary organic chemistry. Since researchers with various scientific backgrounds are entering this interdisciplinary field, different parameters and methods are reported to describe the experiments. The variation in the reported parameters can lead to problems with the reproducibility of the reported electroorganic syntheses. As an example, parameters such as current density or electrode distance are in some cases more significant than often anticipated. This Minireview provides guidelines on reporting electrosyntheti…

Dehydrogenative Anodic Cyanation Reaction of Phenols in Benzylic Positions

Development and Scale-Up of the Electrochemical Dehalogenation for the Synthesis of a Key Intermediate for NS5A Inhibitors

The electrochemical 2-fold dehalogenation of a spirocyclopropane-proline derivative at leaded bronze was scaled-up in a divided batch-type electrolysis cell in good yield and excellent selectivity. The upscaling via a flow electrolysis cell was also successful. Conditions were elaborated employing a single cell passage for complete conversion. The keys here are the direct cooling of the cathode and ensuring a good laminar flow.

Microporous Triptycene‐Based Affinity Materials on Quartz Crystal Microbalances for Tracing of Illicit Compounds

Triptycene-based organic molecules of intrinsic microporosity (OMIMs) with extended functionalized π-surfaces are excellent materials for gas sorption and separation. In this study, the affinities of triptycene-based OMIM affinity materials on 195 MHz high-fundamental-frequency quartz crystal microbalances (HFF-QCMs) for hazardous and illicit compounds such as piperonal and (-)-norephedrine were determined. Both new and existing porous triptycene-based affinity materials were investigated, resulting in very high sensitivities and selectivities that could be applied for sensing purposes. Remarkable results were found for safrole - a starting material for illicit compounds such as ecstasy. A …

The Role of Side-Arms for Supramolecular Affinity Materials Based on 9,9′-Spirobifluorenes

An eightfold functionalized D2d-symmetric 9,9' spirobifluorene was condensed with a collection of diketones with elaborated structural features to form three-dimensional supramolecular architectures with active surfaces. Gas sorption measurements by quartz crystal microbalances revealed remarkable indications about the molecular interactions for the application as affinity materials for the detection of volatile organic compounds. Single-crystal X-ray structure analysis further gave insight by packing motifs and for potential host-guest interactions.

Versatile Electrochemical C-H Amination via Zincke Intermediates.

Simply by applying electricity, the amination reaction of a broad variety of arenes, heteroarenes, and benzylic substrates is achieved. Pyridine serves as the nitrogen source and the intermediate cationic species are well-protected from over-oxidation.

Influence of the excitation conditions on the emission behavior of carbon nanodot-based planar microcavities

The authors investigate the influence of the pulse length as well as the repetition rate of the optical excitation on the emission behavior of carbon-nanodot-based planar microcavities.

Metall- und reagensfreie hochselektive anodische Kreuzkupplung von Phenolen

Functionalized planar Bragg grating sensor for the detection of BTX in solvent vapor

We report on an optical planar Bragg grating evanescent wave refractive index sensor functionalized by a simple method against aromatic hydrocarbons such as benzene, toluene and xylene (BTX) in solvent vapor. To functionalize the sensor against BTX, substituted cyclodextrins are applied to the sensor surface using dip coating. Cyclodextrins have a hydrophobic cavity, which favors the accommodation of an organic molecule of appropriate dimensions leading to a non-covalent inclusion complex. The temporal sensor response reveals a multi-exponential rise towards an equilibrium state, whose level is found to be linearly related to the exposed analyte concentration. Taking into account the spectr…

Citric Acid Based Carbon Dots with Amine Type Stabilizers: pH-Specific Luminescence and Quantum Yield Characteristics

We report the synthesis and spectroscopic characteristics of two different sets of carbon dots (CDs) formed by hydrothermal reaction between citric acid and polyethylenimine (PEI) or 2,3-diaminopyridine (DAP). Although the formation of amide-based species and the presence of citrazinic acid type derivates assumed to be responsible for a blue emission is confirmed for both CDs by elemental analysis, infrared spectroscopy, and mass spectrometry, a higher abundance of sp2-hybridized nitrogen is observed for DAP-based CDs, which causes a red-shift of the n-π* absorption band relative to the one of PEI-based CDs. These CD systems possess high photoluminescence quantum yields (QY) of ∼40% and ∼48…

Simple electrochemical reduction of nitrones to amines.

Only electricity is needed for the transformation of nitrones to amines. Such a direct double reduction has not been reported by any sole chemical reagent in a single step process.

A very simple one-pot electrosynthesis of nitrones starting from nitro and aldehyde components

The cathodic treatment of nitroarenes in the presence of aldehydes yields directly and selectively nitrones. Electrolysis can be conducted on a very simple undivided beaker-type cell under constant current conditions. The conversion tolerates multiple bonds, a variety of functional groups and heterocyclic moieties. Competing reductive conversions such as pinacolization are not observed. The green aspects of this electro-conversion are avoidance of metals, an environmentally benign solvent mixture, and stable as well as sustainable carbon electrodes.

Mo-Based Oxidizers as Powerful Tools for the Synthesis of Thia- and Selenaheterocycles.

A highly efficient synthetic protocol for the synthesis of thia- and selenaheterocycles has been developed. By employing a MoCl5 -mediated intramolecular dehydrogenative coupling reaction, a broad variety of structural motifs was isolated in yields up to 94 %. The electrophilic key transformation is tolerated by several labile moieties like halides and tertiary alkyl groups. Due to the use of disulfide or diselenide precursors, a high atom efficiency was achieved.

ChemInform Abstract: Oxidative Cyclization Reaction of 2-Aryl-Substituted Cinnamates to Form Phenanthrene Carboxylates by Using MoCl5.

The reagent mixture MoCl5/TiCl4 is successfully applied for the oxidative cyclization of α-aryl substituted cinnamates to the corresponding phenanthrenes.

Molybdenum Pentachloride Mediated Synthesis of Spirocyclic Compounds by Intramolecular Oxidative Coupling

The oxidative treatment of (m)ethyl 2-aryl cinnamates equipped with methoxy groups in position 4 of the phenyl moiety promote the formation of cyclohexadienone substructures. This dealkylative oxidative C–C coupling gives access to spirocyclic compounds and avoids the construction of the corresponding phenanthrenes. Furthermore, the transformation can be expanded to other spirocyclic systems.

ChemInform Abstract: Modular Access to 9,9-Spirobifluorenes by Oxidative Coupling Using Molybdenum Pentachloride.

The reactions of diarylfluorenes and substrates (III) or (V) result in formation of spirobifluorenes and fluorene derivatives.

Leaded Bronze: An Innovative Lead Substitute for Cathodic Electrosynthesis

Enhancement of the sub-band-gap photoconductivity in ZnO nanowires through surface functionalization with carbon nanodots

We report on the surface functionalization of ZnO nanowire (NW) arrays by attachment of carbon nanodots (C-dots) stabilized by polyethylenimine. The photoconductive properties of the ZnO NWs/C-dots devices were investigated under photoexcitation with photon energies below and above the ZnO band gap. The results indicate an increased photoresponse of the functionalized devices in the visible spectral range, as well as enhanced UV photoconductivity. This is attributed to the fast injection of photoexcited electrons from the C-dots into the conduction band of the ZnO NWs, and the subsequent slower desorption of molecular species from the NW surface, which reduces the surface depletion region i…

Obituary for Prof. Dr. Jun-ichi Yoshida

ChemInform Abstract: Synthesis of Highly Fluorinated 2,2′-Biphenols and 2,2′-Bisanisoles.

The selective Ullmann-type reaction proceeds under solvent-free conditions and tolerates even a bromo substituent.

Electrochemical Formation of 3,5-Diimido-1,2-dithiolanes by Dehydrogenative Coupling

A synthetic approach to the cyclic disulfide moiety of 3,5-diimido-1,2-dithiolane derivatives starting with readily available precursors including the electrochemical coupling of dithioanilides is developed. The electrochemical key step provides sustainable synthetic access in high yields, using a very simple electrolysis setup.

Facile access to foldable redox-active flavin-peptide conjugates

A convenient approach for the synthesis of foldable redox-active flavin peptide conjugates was established. A model β-hairpin oligopeptide motif was utilized to demonstrate that azidolysine side-chains are readily functionalised with an alkyne-bearing flavine derivative. The folding equilibrium of the peptide backbone as well as the redox behaviour of the flavin moieties remains intact after the conjugation.

ChemInform Abstract: Oxidative Transformation of Aryls Using Molybdenum Pentachloride

Molybdenum pentachloride combines a strong Lewis acid character with an unusually high oxidation potential creating a powerful reagent for oxidative transformations. Since the oxidative coupling reaction of aryls is induced at an extraordinarily high reaction rate, a variety of labile groups, e.g. iodo, tert-alkyl, etc., are tolerated on the aromatic core. Furthermore, the co-formed molybdenum salts can either be exploited for template effects to obtain uncommon geometries in a preferred manner, or redox-play starts after aqueous workup. Therefore MoCl5 represents a unique and easily available reagent.

ChemInform Abstract: Versatile Electrochemical C-H Amination via Zincke Intermediates

Inside Cover: Efficient and Stereodivergent Electrochemical Synthesis of Optically Pure Menthylamines (Angew. Chem. Int. Ed. 24/2011)

Front Cover: Metal‐ and Reagent‐Free Anodic Dehydrogenative Cross‐Coupling of Naphthylamines with Phenols (ChemElectroChem 9/2018)

Electrochemical Synthesis of 2-Hydroxy-para-terphenyls by Dehydrogenative Anodic C–C Cross-Coupling Reaction

The anodic C–C cross-coupling reaction provides fast access to a wide range of bi- and terarylic scaffolds by electrochemically mediated arylation reactions. Herein, a metal- and reagent-free electrosynthetic protocol for the synthesis of nonsymmetrical 2-hydroxy-para-teraryl derivatives is presented for the first time. It is scalable, easy to conduct, and allows the use of a broad variety of different functional groups.

Reaction Condition Screening by Using Electrochemical Microreactor: Application to Anodic Phenol-arene C,C Cross-Coupling Reaction in High Acceptor Number Media

The anodic phenol-arene C,C cross-coupling reaction was achieved in inexpensive and sustainable media such as methanol, acetic acid, and formic acid by using an electrochemical microreactor which can provide a better performance to screen reaction conditions than in standard beaker-type electrolysis cells. Especially, formic acid as a reaction medium showed good performance. The total amount of cross-coupling product and homo-coupling products as a by-product was clearly increased as the solvent acceptor number increased. To control the selective oxidation of phenol, addition of methanol was effective.

Cover Feature: Direct Metal‐ and Reagent‐Free Sulfonylation of Phenols with Sodium Sulfinates by Electrosynthesis (Chem. Eur. J. 28/2019)

Cover Picture: Oxidative Cyclization Reaction of 2-Aryl-Substituted Cinnamates To Form Phenanthrene Carboxylates by Using MoCl5 (Chem. Eur. J. 39/2014)

A solvent-directed stereoselective and electrocatalytic synthesis of diisoeugenol.

A stereoselective and electrocatalytic coupling reaction of isoeugenol has been reported for the first time in a 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP)/boron-doped diamond (BDD) electrode system. This particular C-C bond formation and diastereoselectivity is driven by a solvate interaction between the radical species and another isoeugenol molecule. Due to an electrocatalytic cycle, only understoichiometric amounts of charge are necessary. Since electric current is directly employed as the oxidant, the reaction is metal and reagent-free. In addition, the electrolysis can be conducted in a very simple undivided beaker-type cell under constant current conditions. Therefore, the protocol is …

The Generation Effect: Cavity Accessibility in Dense‐Shell Polyphenylene Dendrimers

Size exclusion is a widespread phenomenon in supra- and macromolecular chemistry. Herein, the size exclusion properties of polyphenylene dendrimers on the surface of high fundamental frequency quartz crystal microbalances are reported. For this purpose, a new dense fifth-generation polyphenylene dendrimer, which was previously not possible owing to the high steric demand of the dendron arms, was synthesized. By increasing the volume and size of subjected analytes an affinity shift from smaller to larger dendrimers can be obtained.

Cover Picture: Bis(2,2′‐biphenoxy)borates for Electrochemical Double‐Layer Capacitor Electrolytes (Chem. Eur. J. 11/2011)

Planar Bragg Grating Sensor for the Detection of CFC-11

We demonstrate the fabrication of a highly sensitive opto-chemical sensor system based on cyclodextrin derivative functionalized planar Bragg gratings for an online in-situ detection and measurement of the environmentally harmful propellant trichlorofluoromethane in real-time.

Stereoselective cathodic synthesis of 8-substituted (1R,3R,4S)-menthylamines.

The electrochemical generation of menthylamines from the corresponding menthone oximes equipped with an additional substituent in position 8 is described. Due to 1,3-diaxial interactions a pronounced diastereoselectivity for the menthylamines is found.

Unexpected high robustness of electrochemical cross-coupling for a broad range of current density

Solvent effect enables electrosynthesis of organic compounds with strong variation of electric current at constant efficacy.

Solvent-Adaptive Behavior of Oligospirobifluorenes at the Surface of Quartz Crystal Microbalances-A Conformational Process

Oligospirobifluorenes represent promising building blocks for the generation of microporous sensor materials based on their restricted flexibility. The contact with specific solvents leads to a change of the three-dimensional spirobifluorene structure. The single fluorene moieties unfold to an open structure with an increased volume due to intermolecular interactions with the solvent, detectable by NMR spectroscopy. The induced microporosity was further investigated by affinity comparisons of aromatic analytes with high fundamental frequency quartz crystal microbalances.

ChemInform Abstract: Molybdenum Pentachloride. A Multifaceted Reagent for Efficient Coupling of Aromatics

Scaffold-Optimized Dendrimers for the Detection of the Triacetone Triperoxide Explosive Using Quartz Crystal Microbalances

Challenges in Electroorganic Synthesis

Synthesis of 9,9′-Spirobifluorenes and 4,5-Diaza-9,9′-spirobifluorenes and Their Application as Affinity Materials for Quartz Crystal Microbalances

Two different classes of aza analogues of 9,9'-spirobifluorenes have been synthesized. These were obtained by either furnishing the spirobifluorene with additional pyridyl moieties or by installing the aza function directly into the spirobifluorene core. These structurally rigid compounds were then evaluated as affinity materials for quartz crystal microbalances and proved to be highly potent for the detection of volatile organic compounds.

Sustainable and cost-efficient electro-synthesis of formamidine acetate from cyanamide in aqueous acidic electrolyte

Formamidine represents a versatile building block in synthetic organic chemistry. We developed a new electrochemical synthesis of formamidine acetate by cathodic reduction of cyanamide in an aqueous electrolyte and in high yield. The crude product could be used for further conversions, such as to pyrimidines without purification. Compared to established synthetic routes neither prior processing of cyanamide was necessary, nor precious transition-metal catalyst were required, nor any reagent waste was produced, and only biocompatible and sustainable solvents were employed for this process, following the requirements of green chemistry.

Front Cover: Electrosynthetic Screening and Modern Optimization Strategies for Electrosynthesis of Highly Value‐added Products (ChemElectroChem 14/2021)

Cover Feature: Metal‐ and Reagent‐Free Electrochemical Synthesis of Alkyl Arylsulfonates in a Multi‐Component Reaction (Chem. Eur. J. 38/2020)

Anodic Formation of Aryl Mesylates through Dehydrogenative Coupling Reaction

Electrosynthesis of Stable Betulin‐Derived Nitrile Oxides and their Application in Synthesis of Cytostatic Lupane‐Type Triterpenoid‐Isoxazole Conjugates

Versatile oxidative approach to carbazoles and related compounds using MoCl5.

The unique oxidizing power of molybdenum pentachloride provides an easy to perform, versatile, and high yielding method to construct carbazoles and the corresponding dibenzo analogues of thiophene, furan, and selenophene. The coupling reaction tolerates a variety of functional groups. The synthesis is highly modular. By this approach a precursor for the naturally occurring carbazole koenigicine was prepared.

Cover Picture: Metal‐ and Reagent‐Free Highly Selective Anodic Cross‐Coupling Reaction of Phenols (Angew. Chem. Int. Ed. 20/2014)

Front Cover: Electrochemical Synthesis of Fluorinated Orthoesters from 1,3‐Benzodioxoles (ChemistryOpen 9/2019)

The Front Cover shows the robustness achieved by the installation of fluorinated alcohols on 1,3‐benzodioxoles, which appears like the shield of a knight protecting the obtained orthoesters against acids and bases. The simple protocol allows access to interesting compounds, whose lipophilicity is tremendously increased by the incorporation of fluorinated groups. This makes it possible to adjust the physicochemical properties of the biologically active 1,3‐benzodioxole motif. The surprisingly high stability against acids and bases gives rise to subsequent functionalizations or direct application in medicinal or agrochemistry. More information can be found in the Communication by J. L. Röckl …

Crystal structure of ethyl 2-(di-eth-oxy-phosphor-yl)-2-(2,3,4-tri-meth-oxy-phen-yl)acetate.

The title compound, C17H27O8P, was prepared by Michaelis–Arbuzov reaction of ethyl 2-bromo-2-(2,3,4-trimethoxyphenyl)acetate and triethyl phosphite. Such compounds rarely crystallize, but single crystals were recovered after the initial oil was left for approximately 10 years. The bond angle of thesp3-hybridized C atom connecting the benzene derivative with the phospho unit is widened marginally [112.5 (2)°]. The terminal P—O bond length of 1.464 (2) Å clearly indicates a double bond, whereas the two O atoms of the ethoxy groups connected to the phosphorous atom have bond lengths of 1.580 (2) Å and 1.581 (3) Å. The three methoxy groups emerge out of the benzene-ring plane due to steric hind…

Insights into the Mechanism of Anodic N–N Bond Formation by Dehydrogenative Coupling

The electrochemical synthesis of pyrazolidine-3,5-diones and benzoxazoles by N-N bond formation and C,O linkage, respectively, represents an easy access to medicinally relevant structures. Electrochemistry as a key technology ensures a safe and sustainable approach. We gained insights in the mechanism of these reactions by combining cyclovoltammetric and synthetic studies. The electron-transfer behavior of anilides and dianilides was studied and led to the following conclusion: The N-N bond formation involves a diradical as intermediate, whereas the benzoxazole formation is based on a cationic mechanism. Besides these studies, we developed a synthetic route to mixed dianilides as starting m…

Anodic Degradation of Lignin at Active Transition Metal-based Alloys and Performance-enhanced Anodes

ChemInform Abstract: Molybdenum Pentachloride Mediated Synthesis of Spirocyclic Compounds by Intramolecular Oxidative Coupling.

Oxidative treatment of 4-methoxy substituted 2-aryl cinnamates leads to an dealkylative C—C coupling and gives access to spirocyclic compounds.

Active Molybdenum‐Based Anode for Dehydrogenative Coupling Reactions

A new and powerful active anode system that can be operated in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) has been discovered. In HFIP the molybdenum anode forms a compact, conductive, and electroactive layer of higher-valent molybdenum species. This system can replace powerful but stoichiometrically required MoV reagents for the dehydrogenative coupling of aryls. This electrolytic reaction is more sustainable and allows the conversion of a broad scope of activated arenes.

Fluorocyclization of N-Propargylamides to Oxazoles by Electrochemically Generated ArIF2

A sustainable synthesis of 5-fluoromethyl-2-oxazoles by use of electrochemistry has been demonstrated. Hypervalent ArIF2 is generated by direct electrochemical oxidation of iodoarene ArI in Et3N·5HF and mediates the fluorocyclization of N-propargylamides to 5-fluoromethyl-2-oxazoles. The stoichiometry in ArI turned out to be a key parameter in controlling the product selectivity. This electrochemical protocol provides access to fluorinated oxazoles starting from simply available N-propargylamides with yields up to 65% and offers a green alternative over conventional reagent-based approaches.

ChemInform Abstract: Versatile Oxidative Approach to Carbazoles and Related Compounds Using MoCl5.

Oxidative intramolecular coupling of tertiary amines with at least two electron-rich arenes gives carbazoles in good to excellent yields.

Cover Picture: Selective Synthesis of Partially Protected Nonsymmetric Biphenols by Reagent‐ and Metal‐Free Anodic Cross‐Coupling Reaction (Angew. Chem. Int. Ed. 39/2016)

Electrochemical formation of N,N′-diarylhydrazines by dehydrogenative N–N homocoupling reaction

Hydrazines represent a class of compounds of high interest due to their applicability as versatile starting materials in many important transformations. Herein, we report a synthetic approach to hydrazine derivatives using commercially available anilines and an anodic dehydrogenative N-N coupling reaction as the key step.

Applicability of a Polymerized Ionic Liquid/Carbon Nanoparticle Composite Electrolyte to Reductive Cyclization and Dimerization Reactions

Abstract Recently, a reusable polymerized ionic liquid/carbon nanoparticle composite electrolyte was developed and effectively applied to a variety of oxidative transformations. The efficient recovery of the composite material and its application in subsequent electroorganic conversions without sacrificing yield adds to the sustainability of the protocol. Herein, we describe our efforts to expand the operational window of the composite electrolyte to include cathodically initiated processes occurring at potentials up to −2.6 V. The results indicate that the composite electrolyte is applicable to reductive processes, but the scope of transformations appears to be limited.

Electrochemical Synthesis of 5-Aryl-phenanthridin-6-one by Dehydrogenative N,C Bond Formation.

Currently, the general synthesis of 5-aryl-phenanthridin-6-ones relies on the involvement of metal catalysis. Despite the urgent demand for green alternatives, avoiding synthetic routes that require transition metals for key roles is still challenging. Electrochemical efforts employing a constant potential protocol in divided cells revealed a possible alternative to the catalytic approach. A constant current protocol, undivided cells, and a remarkably low supporting electrolyte concentration enable a novel access to N-aryl-phenanthridin-6-ones by anodic N,C bond formation using directly generated amidyl radicals. Easy accessible starting materials, a broad scope of applicable functional gro…

Synthesis of highly functionalized 9,10-phenanthrenequinones by oxidative coupling using MoCl5.

The strong oxidative power of molybdenum pentachloride gives rise to an efficient oxidative C-C bond formation of benzil derivatives to the corresponding 9,10-phenanthrenequinones. A highly complementary method to previous approaches was developed. The required derivatives are accessible in a modular fashion and in excellent yields. By this approach the orchid-derived natural product cypripediquinone A was synthesized for the first time.

Merging shuttle reactions and paired electrolysis for reversible vicinal dihalogenations

Vicinal dibromides and dichlorides are important commodity chemicals and indispensable synthetic intermediates in modern chemistry that are traditionally synthesized using hazardous elemental chlorine and bromine. Meanwhile, the environmental persistence of halogenated pollutants necessitates improved approaches to accelerate their remediation. Here, we introduce an electrochemically assisted shuttle (e-shuttle) paradigm for the facile and scalable interconversion of alkenes and vicinal dihalides, a class of reactions that can be used both to synthesize useful dihalogenated molecules from simple alkenes and to recycle waste material through retro-dihalogenation. The reaction is demonstrated…

Renaissance of Electrosynthetic Methods for the Construction of Complex Molecules

Current affairs: Efficient N,N dimerization by using an electric current is a recent powerful example of preparative electrosynthesis where conventional reagents fail. The general and practical nature of this method as well as other applications will breathe new life into the electroorganic synthesis of complex molecules.

(-)-Isosteviol as a Versatile Ex-Chiral-Pool Building Block for Organic Chemistry

(–)-Isosteviol is readily available in large quantities by the acidic treatment of a common alternative sweetener. The two functional groups of (–)-isosteviol are presented on the same side of the ent-beyerane scaffold with a mutual C–C distance of about 7 A. Their unique concave arrangement experiences a strong asymmetric environment due to an adjacent methyl group. Consequently, this building block has found several applications in supramolecular chemistry and organocatalysis. These areas and the chemical modification of this scaffold as well as its biological activity are surveyed.

Metal‐Free Electrochemical Synthesis of Sulfonamides Directly from (Hetero)arenes, SO2, and Amines

Abstract Sulfonamides are among the most important chemical motifs in pharmaceuticals and agrochemicals. However, there is no methodology to directly introduce the sulfonamide group to a non‐prefunctionalized aromatic compound. Herein, we present the first dehydrogenative electrochemical sulfonamide synthesis protocol by exploiting the inherent reactivity of (hetero)arenes in a highly convergent reaction with SO2 and amines via amidosulfinate intermediate. The amidosulfinate serves a dual role as reactant and supporting electrolyte. Direct anodic oxidation of the aromatic compound triggers the reaction, followed by nucleophilic attack of the amidosulfinate. Boron‐doped diamond (BDD) electro…

Titelbild: Selektive Synthese teilgeschützter unsymmetrischer Biphenole durch reagens‐ und metallfreie anodische Kreuzkupplung (Angew. Chem. 39/2016)

Hybrid LEDs based on ZnO nanowire structures

Abstract This paper summarized the research, development, and state of the art of hybrid ZnO nanowire LEDs, in which electroluminescence is generated at the junction between n-type doped ZnO nanowire structures and specific p-type doped polymers (in particular PEDOT, PEDOT:PSS, or PFO). Different device architectures will be reviewed and discussed with a particular emphasis on the electronic transport through the hybrid structures and the microscopic processes of light emission. Finally, a gas-phase deposition technique for conductive polymers will be presented which might help improve the performance of hybrid ZnO nanowire LEDs in the future.

Challenges in the Electrochemical Synthesis of Si 2 Cl 6 Starting from Tetrachlorosilane and Trichlorosilane

Highly Sensitive Detection of Naphthalene in Solvent Vapor Using a Functionalized PBG Refractive Index Sensor

We report an optical refractive index sensor system based on a planar Bragg grating which is functionalized by substituted γ-cyclodextrin to determine low concentrations of naphthalene in solvent vapor. The sensor system exhibits a quasi-instantaneous shift of the Bragg wavelength and is therefore capable for online detection. The overall shift of the Bragg wavelength reveals a linear relationship to the analyte concentration with a gradient of 12.5 ± 1.5 pm/ppm. Due to the spectral resolution and repeatability of the interrogation system, this corresponds to acquisition steps of 80 ppb. Taking into account the experimentally detected signal noise a minimum detection limit of 0.48 ± 0.05 pp…

Electrochemical synthesis of sulfamides.

Herein we demonstrate the first electrochemical synthesis protocol of symmetrical sulfamides directly from anilines and SO2 mediated by iodide. Sulfamides are an emerging functional group in drug design. Highlights are the direct use of SO2 from a stock solution and no necessity of any supporting electrolyte. Overall, the reaction has been demonstrated for 15 examples with yields up to 93%.

ChemInform Abstract: Electrochemical Screening for Electroorganic Synthesis

Installation of Amine Moieties into a Polycyclic Anodic Product Derived from 2,4-Dimethylphenol

When 2,4-dimethylphenol is anodically treated, a dehydrotetramer with four contiguous stereocentres is readily obtained on a multi-gram scale. The substitution of a 2,4-dimethyl-phenoxy fragment by several amines was demonstrated, and the best results were obtained with primary amines. Optically pure α-chiral aliphatic amines yield diastereomeric mixtures that can be separated in most cases. The basic amine causes a partial hemiketal-opening of the bisbenzofuran moiety leading to an equilibrium within an α,β-unsaturated cyclohexenone. This dynamic behaviour occurs on the time scale of NMR spectroscopy and is also found by X-ray analysis providing a consistent picture.

Single and Twofold Metal- and Reagent-Free Anodic C-C Cross-Coupling of Phenols with Thiophenes.

The first electrochemical dehydrogenative C-C cross-coupling of thiophenes with phenols has been realized. This sustainable and very simple to perform anodic coupling reaction enables access to two classes of compounds of significant interest. The scope for electrochemical C-H-activating cross-coupling reactions was expanded to sulfur heterocycles. Previously, only various benzoid aromatic systems could be converted, while the application of heterocycles was not successful in the electrochemical C-H-activating cross-coupling reaction. Here, reagent- and metal-free reaction conditions offer a sustainable electrochemical pathway that provides an attractive synthetic method to a broad variety …

Direct electrochemical generation of organic carbonates by dehydrogenative coupling.

Organic carbonates are an important source for polycarbonate synthesis. However, their synthesis generally requires phosgene, sophisticated catalysts, harsh reaction conditions, or other highly reactive chemicals. We present the first direct electrochemical generation of mesityl methyl carbonate by C–H activation. Although this reaction pathway is still challenging concerning scope and efficiency, it outlines a new strategy for carbonate generation.

Novel supramolecular affinity materials based on (−)-isosteviol as molecular templates

The readily available ex-chiral-pool building block (−)-isosteviol was combined with the C3-symmetric platforms hexahydroxytriphenylene and hexaaminotriptycene providing large and rigid molecular architectures. Because of the persistent cavities these scaffolds are very potent supramolecular affinity materials for head space analysis by quartz crystal microbalances. The scaffolds serve in particular as templates for tracing air-borne arenes at low concentration. The affinities of the synthesized materials towards different air-borne arenes were determined by 200 MHz quartz crystal microbalances.

Process Development for Wet-Chemical Surface Functionalization of Gallium Arsenide Based Nanowires

ChemInform Abstract: Metal- and Reagent-Free Highly Selective Anodic Cross-Coupling Reaction of Phenols.

Boron-doped diamond electrodes allow the direct anodic cross-coupling of phenols in hexafluoroisopropanol without using leaving functions or protecting groups.

ChemInform Abstract: Palladium-Catalyzed Domino C-H/N-H Functionalization: An Efficient Approach to Nitrogen-Bridged Heteroacenes.

Palladium-catalyzed domino CH/NH functionalization for the synthesis of novel nitrogen-bridged thienoacenes and 10H-benzo[4,5]thieno[3,2-b]indole derivatives from dihaloarene is reported. This domino sequence consists of initial CH functionalization of the benzo[b]thiophene moiety, followed by Buchwald–Hartwig coupling. This transformation is also useful for the synthesis of highly π-extended compounds.

Renaissance elektrochemischer Methoden zum Aufbau komplexer Moleküle

Regioselective Metal- and Reagent-Free Arylation of Benzothiophenes by Dehydrogenative Electrosynthesis.

A novel strategy for the synthesis of biaryls consisting of a benzothiophene and a phenol moiety is reported. These heterobiaryls are of utmost interest for pharmaceutical, biological, and high-performance optoelectronic applications. The metal- and reagent-free, electrosynthetic, and highly efficient method enables the generation of 2- and 3-(hydroxyphenyl)benzo[b]thiophenes in a regioselective fashion. The described one-step synthesis is easy to conduct, scalable, and inherently safe. The products are afforded in high yields of up to 88 % and with exquisite selectivity. The reaction also features a broad scope and tolerates a large variety of functional groups.

Reagens- und metallfreie anodische C-C-Kreuzkupplung von Anilinderivaten

Vorgestellt wird die oxidative Kreuzkupplung von Anilinderivaten zu 2,2′-Diaminobiarylen. Der Oxidationsschritt wird elektrochemisch durchgefuhrt, ohne die Notwendigkeit von Metallen und Reagenzien. Ein breites Spektrum an Biphenyldiaminen konnte hergestellt werden. Die besten Resultate wurden mit Glaskohlenstoff als Anodenmaterial erhalten. Die elektrochemische Umsetzung kann problemlos in einer ungeteilten Zelle bei leicht erhohten Temperaturen durchgefuhrt werden. Auserdem wurden gebrauchliche, auf Carbonsauren basierende, Schutzgruppen verwendet, die nach der Kreuzkupplung unter milden Bedingungen selektiv abgespalten werden konnen. Auf diese Weise erhalt man schnell und effizient Zugan…

The sustainable synthesis of levetiracetam by an enzymatic dynamic kinetic resolution and an ex-cell anodic oxidation

Levetiracetam is an active pharmaceutical ingredient widely used to treat epilepsy. We describe a new synthesis of levetiracetam by a dynamic kinetic resolution and a ruthenium-catalysed ex-cell anodic oxidation. For the enzymatic resolution, we tailored a high throughput screening method to identify Comamonas testosteroni nitrile hydratase variants with high (S)-selectivity and activity. Racemic nitrile was applied in a fed-batch reaction and was hydrated to (S)-(pyrrolidine-1-yl)butaneamide. For the subsequent oxidation to levetiracetam, we developed a ligand-free ruthenium-catalysed method at a low catalyst loading. The oxidant was electrochemically generated in 86% yield. This route pro…

A Novel Cathode Material for Cathodic Dehalogenation of 1,1-Dibromo Cyclopropane Derivatives.

Leaded bronze turned out to be an excellent cathode material for the dehalogenation reaction of cyclopropanes without affecting the strained molecular entity. With this particular alloy, beneficial properties of lead cathodes are conserved, whereas the corrosion of cathode is efficiently suppressed. The solvent in the electrolyte determines whether a complete debromination reaction is achieved or if the process can be selectively stopped at the monobromo cyclopropane intermediate. The electroorganic conversion tolerates a variety of functional groups and can be conducted at rather complex substrates like cyclosporine A. This approach allows the sustainable preparation of cyclopropane deriva…

Rücktitelbild: Eine regio- und diastereoselektive anodische Aryl-Aryl-Kupplung in der biomimetischen Totalsynthese von (−)-Thebain (Angew. Chem. 34/2018)

Synthesis and Isolation of Enantiomerically Enriched Cyclopenta[b]benzofurans Based on Products from Anodic Oxidation of 2,4-Dimethylphenol

The anodic treatment of 2,4-dimethylphenol offers a powerful and direct method for the construction of a dehydrotetramer with four contiguous stereocentres on a multigram scale. The installation of propellanes on this scaffold using enantiomerically pure carbonyl compounds leads to a mixture of diastereomers. This mixture is easily separable using standard chromatography and gives rise to optically pure cyclopenta[b]benzofurans which are important scaffolds in a variety of natural products. The synthesis is easy to perform and allows a reliable access to chiral compounds with very high enantiomeric excess. It was possible to determine the absolute configuration of these compounds by compari…

Electrochemical synthesis on boron-doped diamond

Abstract Boron-doped diamond (BDD) is a novel and innovative electrode material. In protic media and particular aqueous electrolytes BDD exhibits a large over potential for the evolution of molecular hydrogen and oxygen. The large chemical window allows a variety of electrochemical conversions to be conducted. The anodic process treatment generates oxyl species directly which are known to be extremely reactive. Usually, the electrochemical mineralization of the organic components in the electrolyte occurs. However, with control of the reactivity of these intermediates the use in electroorganic synthesis can be realized. Until today mostly anodic conversions have been studied at BDD. Since h…

Cover Feature: New Approach to 1,4-Benzoxazin-3-ones by Electrochemical C−H Amination (Chem. Eur. J. 50/2017)

A Regio- and Diastereoselective Anodic Aryl-Aryl Coupling in the Biomimetic Total Synthesis of (-)-Thebaine.

The biosynthesis of thebaine is based on the regioselective, intramolecular, oxidative coupling of (R)-reticuline. For decades, chemists have sought to mimic this coupling by using stoichiometric oxidants. However, all approaches to date have suffered from low yields or the formation of undesired regioisomers. Electrochemistry would represent a sustainable alternative in this respect but all attempts to accomplish an electrochemical synthesis of thebaine have failed so far. Herein, a regio- and diastereoselective anodic coupling of 3',4',5'-trioxygenated laudanosine derivatives is presented, which finally enables electrochemical access to (-)-thebaine.

Dehydrogenative Anodic C−C Coupling of Phenols Bearing Electron‐Withdrawing Groups

Abstract We herein present a metal‐free, electrosynthetic method that enables the direct dehydrogenative coupling reactions of phenols carrying electron‐withdrawing groups for the first time. The reactions are easy to conduct and scalable, as they are carried out in undivided cells and obviate the necessity for additional supporting electrolyte. As such, this conversion is efficient, practical, and thereby environmentally friendly, as production of waste is minimized. The method features a broad substrate scope, and a variety of functional groups are tolerated, providing easy access to precursors for novel polydentate ligands and even heterocycles such as dibenzofurans.

Electrochemical Deoxygenation of Aromatic Amides and Sulfoxides

The electrochemical deoxygenation of a broad range of aromatic amides was achieved under mild conditions on lead cathodes. Under the optimized reaction conditions, acetal, thienyl, and ether moieties are tolerated. Furthermore, the reduction protocol can be applied to aromatic and aliphatic sulfoxides to obtain the corresponding sulfides. For both aromatic amides and sulfoxides, the deoxygenation reaction ensues without the use of expensive catalysts or hazardous reducing agents. Owing to the high selectivity of the process, simple extraction is sufficient to isolate the product from the substrate. The straightforward purification protocol, the coformation of water, and the use of electric …

Selective and Scalable Electrosynthesis of 2H-2-(Aryl)-benzo[d]-1,2,3-triazoles and Their N-Oxides by Using Leaded Bronze Cathodes.

Abstract Electrosynthesis of 2H‐2‐(aryl)benzo[d]‐1,2,3‐triazoles and their N‐oxides from 2‐nitroazobenzene derivatives is reported. The electrolysis is conducted in a very simple undivided cell under constant current conditions with a leaded bronze cathode and a glassy carbon anode. The product distribution between 2H‐2‐(aryl)benzo[d]‐1,2,3‐triazoles and their N‐oxides can be guided by simply controlling the current density and the amount of the charge applied. The reaction tolerates several sensitive functional groups in reductive electrochemistry. The usefulness and the applicability of the synthetic method is demonstrated by a formal synthesis of an antiviral compound.

High-Temperature Electrolysis of Kraft Lignin for Selective Vanillin Formation

Lignin represents the largest renewable resource of aromatic moieties on earth and harbors a huge potential as a sustainable feedstock for the synthesis of biobased aromatic fine chemicals. Due to the complex, heterogeneous, and robust chemical structure of the biopolymer, the valorization is associated with significant challenges. Unfortunately, technical lignins, which are a large side stream of the pulp and paper industries, are mainly thermally exploited. In this study, technical Kraft lignin was selectively electrochemically depolymerized to the aroma chemical vanillin. Using electricity, toxic and/or expensive oxidizers could be replaced. The electrodegradation of Kraft lignin was per…

ChemInform Abstract: Electroorganic Synthesis of Nitriles via a Halogen-Free Domino Oxidation-Reduction Sequence.

A direct electroorganic sequence yielding nitriles from oximes in undivided cells is reported. Despite the fact that intermediate nitrile oxides might be formed, the method is viable to prepare benzonitriles without substituents ortho to the aldoxime moiety. This constant current method is easy to perform for a broad scope of substrates and employs common electrodes, such as graphite and lead.

Surface Pretreatment Boosts the Performance of Supramolecular Affinity Materials on Quartz Crystal Microbalances for Sensor Applications

A Teflon-like coating is the key for the boost in sensitivity of quartz microbalances for the tracing of airborne analytes. Since the undesired signals for the interfering compounds are suppressed and the ones for the targeted compounds (e.g., peroxide explosives) are enhanced, the PCA output is improved.

Electrosynthesis 2.0 in 1,1,1,3,3,3-hexafluoroisopropanol/amine mixtures

Unusual redox play of Mo(V/IV) during oxidative aryl–aryl coupling

The oxidative treatment of a suitable 1,3-diarylpropene precursor by MoCl5 causes a series of redox steps yielding a dimer of dibenzo[a,c]cycloheptene. After the oxidative aryl–aryl bond formation, a C,H activation occurs providing a tropylium intermediate. Upon aqueous workup the metal waste acts as reductive media generating the dimer in an almost quantitative manner. The oxidative generation of the tropylium species as well as the subsequent redox play by the metal waste is unique and unprecedented. The dimeric compound can be oxidatively cleaved and subsequently decarboxylated providing the key intermediate of a previous synthesis of metasequirin-B derivatives.

Electrosynthesis and electrochemistry

Since the pioneering work of Kolbe, electrochemistry and electrosynthetic methods have been a part of the repertoire of the organic synthesis toolbox [1–2]. In general, only electrons are employed as reagents or the reagents are electrochemically regenerated. Consequently, waste can be avoided, and limited resources can be used in a careful and economic manner. Because alternative reaction pathways are employed by electrosynthetic methods, scarce and toxic elements can be replaced or are not required at all [3]. Moreover, in the foreseeable future regenerative sources of electricity, for example, photovoltaics and wind power, will provide a surplus of electricity as the current unsteady sup…

Synthesis of Highly Functionalized N , N ‐Diarylamides by an Anodic C, N ‐Coupling Reaction

We report an innovative, sustainable and straightforward protocol for the synthesis of N,N-diarylamides equipped with nonprotected hydroxyl groups by using electrosynthesis. The concept allows the application of various substrates furnishing diarylamides with yields up to 57 % within a single and direct electrolytic protocol. The method is thereby easy to conduct in an undivided cell with constant current conditions offering a versatile and short-cut alternative to conventional pathways.

Cover Picture: Solvent-Adaptive Behavior of Oligospirobifluorenes at the Surface of Quartz Crystal Microbalances-A Conformational Process (ChemPlusChem 8/2017)

Powerful Fluoroalkoxy Molybdenum(V) Reagent for Selective Oxidative Arene Coupling Reaction

We introduce the novel fluoroalkoxy molybdenum(V) reagent 1 which has superior reactivity and selectivity in comparison to MoCl5 or the MoCl5 /TiCl4 reagent mixture in the oxidative coupling reactions of aryls. Common side reactions, such as chlorination and/or oligomer formation, are drastically diminished creating a powerful and useful reagent for oxidative coupling. Theoretical treatment of the reagent interaction with 1,2-dimethoxybenzene-type substrates indicates an inner-sphere electron transfer followed by a radical cationic reaction pathway for the oxidative-coupling process. EPR spectroscopic and electrochemical studies, X-ray analyses, computational investigations, and the experim…

ChemInform Abstract: Synthesis of Highly Functionalized 9,10-Phenanthrenequinones by Oxidative Coupling Using MoCl5.

An efficient method to prepare functionalized 9,10-phenanthrenequinones including the natural cypripediquinone A (VIIIa) is reported.

Titelbild: Metall- und reagensfreie hochselektive anodische Kreuzkupplung von Phenolen (Angew. Chem. 20/2014)

Trends of Organic Electrosynthesis by Using Boron-Doped Diamond Electrodes

The electro-organic synthesis is currently experiencing a renaissance due to the tremendous contributions of various electrocatalytic materials as well as the use of electric current as an inexpensive and suitable reagent to drive the electrosynthetic transformations, avoiding conventional chemical oxidizers or reducing agents. Consequently, electrosynthesis has a significant technical impact, because these processes can be easily scaled up, benefiting from advantages such as versatility, environmental compatibility (possibility of recovering and recycling non-converted substrates), automation (switching on or off electric current), inherent safety and potential cost effectiveness among oth…

Elektrochemische allylische Oxidation von Olefinen: nachhaltig und sicher

Efficient electroorganic synthesis of 2,3,6,7,10,11-hexahydroxytriphenylene derivatives

2,3,6,7,10,11-Hexahydroxytriphenylene of good quality and purity can be obtained via anodic treatment of catechol ketals and subsequent acidic hydrolysis. The electrolysis is conducted in propylene carbonate circumventing toxic and expensive acetonitrile. The protocol is simple to perform and superior to other chemical or electrochemical methods. The key of the method is based on the low solubility of the anodically trimerized product. The shift of potentials is supported by cyclic voltammetry studies.

Solvent Control in Electro-Organic Synthesis

Exploiting the solvent control within electro-organic conversions is a far underestimated parameter in prep-scale electrolysis. The beneficial application in several transformations is outlined and in particular discussed for the dehydrogenative coupling of arenes and heteroarenes. This simple electrolytic strategy in fluorinated solvents allows the modulation of the substrate’s nucleophilicity and the stabilization of the intermediates as well as of the final product from over-oxidation.1 Introduction2 Solvent Effects in Kolbe Electrolysis and Anodic Fluorination3 Unique Solvent Effects of 1,1,1,3,3,3-Hexafluoropropan-2-ol (HFIP)4 Anodic Dehydrogenative Coupling Reactions with Use of HFIP …

Electrifying Organic Synthesis

Abstract The direct synthetic organic use of electricity is currently experiencing a renaissance. More synthetically oriented laboratories working in this area are exploiting both novel and more traditional concepts, paving the way to broader applications of this niche technology. As only electrons serve as reagents, the generation of reagent waste is efficiently avoided. Moreover, stoichiometric reagents can be regenerated and allow a transformation to be conducted in an electrocatalytic fashion. However, the application of electroorganic transformations is more than minimizing the waste footprint, it rather gives rise to inherently safe processes, reduces the number of steps of many synth…

Electrochemical oxo-functionalisation of cyclic alkanes and alkenes using nitrate and oxygen

Abstract Direct functionalization of C(sp3)–H bonds allows a fast, synthetic access to valuable products, starting from simple petrochemicals. Chemical transformation of inactivated methylene groups, however, remains challenging for organic synthesis. Here, we present a general electrochemical method for the oxidation of C(sp3)–H and C(sp2)–H bonds, in which cyclic alkanes and (cyclic) olefins are converted into cycloaliphatic ketones as well as aliphatic (di)carboxylic acids. This resource-friendly method is based on nitrate salts in a dual role as anodic mediator and supporting electrolyte, which can be fully recovered and recycled. Reduction of molecular oxygen as cathodic counter reacti…

Electrosynthetic screening and modern optimization strategies for electrosynthesis of highly value-added products

Electrochemical Installation of CFH 2 −, CF 2 H−, CF 3 −, and Perfluoroalkyl Groups into Small Organic Molecules

Electrosynthesis can be considered a powerful and sustainable methodology for the synthesis of small organic molecules. Due to its intrinsic ability to generate highly reactive species under mild conditions by anodic oxidation or cathodic reduction, electrosynthesis is particularly interesting for otherwise challenging transformations. One such challenge is the installation of fluorinated alkyl groups, which has gained significant attention in medicinal chemistry and material science due to their unique physicochemical features. Unsurprisingly, several electrochemical fluoroalkylation methods have been established. In this review, we survey recent developments and established methods in the…

Synthesis of Highly Fluorinated 2,2′-Biphenols and 2,2′-Bisanisoles

Multiply fluorine-substituted iodo anisoles are efficiently coupled in an Ullmann-type reaction to provide the corresponding bisanisoles. The coupling is selective and even tolerates bromo moieties. Subsequent deprotection of hydroxy groups gives access to highly fluorinated biphenols.

Frontispiz: Metallfreie, elektrochemische Synthese von Sulfonamiden direkt aus (Hetero)arenen, SO 2 und Aminen

Electrochemical Arylation Reaction

Arylated products are found in various fields of chemistry and represent essential entities for many applications. Therefore, the formation of this structural feature represents a central issue of contemporary organic synthesis. By the action of electricity the necessity of leaving groups, metal catalysts, stoichiometric oxidizers, or reducing agents can be omitted in part or even completely. The replacement of conventional reagents by sustainable electricity not only will be environmentally benign but also allows significant short cuts in electrochemical synthesis. In addition, this methodology can be considered as inherently safe. The current survey is organized in cathodic and anodic con…

Highly Modular Flow Cell for Electroorganic Synthesis

A highly modular electrochemical flow cell and its application in electroorganic synthesis is reported. This innovative setup facilitates many aspects: an easy adjustment of electrode distance, quick exchange of electrode material, and the possibility to easily switch between a divided or undivided cell. However, the major benefit of the cell is the exact thermal positioning of the electrode material into a Teflon piece. Thereby, the application of expensive and nonmachinable electrode materials like boron-doped diamond or glassy carbon can easily be realized in flow cells. By this geometry, the maximum surface of such valuable electrode materials is exploited. The cell size can compete wit…

ChemInform Abstract: Selective Synthesis of Partially Protected Nonsymmetric Biphenols by Reagent- and Metal-Free Anodic Cross-Coupling Reaction.

The oxidative cross-coupling of aromatic substrates without the necessity of leaving groups or catalysts is described. The selective formation of partially protected nonsymmetric 2,2'-biphenols via electroorganic synthesis was accomplished with a high yield of isolated product. Since electric current is employed as the terminal oxidant, the reaction is reagent-free; no reagent waste is generated as only electrons are involved. The reaction is conducted in an undivided cell, and is suitable for scale-up and inherently safe. The implementation of O-silyl-protected phenols in this transformation results in both significantly enhanced yields and higher selectivity for the desired nonsymmetric 2…

Get into flow: Design of experiments as a key technique in the optimization of anodic dehydrogenative C,C cross-coupling reaction of phenols in flow electrolyzers

Abstract The optimization of electro-organic reactions poses a challenge due to the various parameters involved. Quite often those parameters are not independent from each other, leading the experimental scientist using linear approaches into an optimization loophole. We report a strategy for the optimization of the anodic oxidative dehydrogenative C,C cross-coupling reactions for the synthesis of biphenols based on Design of Experiments (DoE), which overcomes the drawbacks of linear optimization approaches. Using a fractional design, we increased the yield of a long-time investigated example reaction from 44% up to 85% and point out different suitable reaction conditions through to linear …

Diversity-Oriented Synthesis of Polycyclic Scaffolds by Modification of an Anodic Product Derived from 2,4-Dimethylphenol

Highly selective electrosynthesis of biphenols on graphite electrodes in fluorinated media.

The direct and selective phenol coupling reaction that provides biphenols still represents a challenge in organic synthesis. The recently developed electrosynthesis on boron-doped diamond anodes with fluorinated additives was developed further to allow the application to less-expensive electrodes and fluorinated media. This advanced protocol allows the highly selective anodic phenol coupling reaction on graphite with a broad scope.

Use of Boron‐Doped Diamond Electrodes in Electro‐Organic Synthesis

Reagent- and Metal-Free Anodic C-C Cross-Coupling of Aniline Derivatives.

The dehydrogenative cross-coupling of aniline derivatives to 2,2′-diaminobiaryls is reported. The oxidation is carried out electrochemically, which avoids the use of metals and reagents. A large variety of biphenyldiamines were thus prepared. The best results were obtained when glassy carbon was used as the anode material. The electrosynthetic reaction is easily performed in an undivided cell at slightly elevated temperature. In addition, common amine protecting groups based on carboxylic acids were employed that can be selectively removed under mild conditions after the cross-coupling, which provides quick and efficient access to important building blocks featuring free amine moieties.

Electrochemical Oxidative C – C Bond Formation

Selective and Scalable Dehydrogenative Electrochemical Synthesis of 3,3′,5,5′-Tetramethyl-2,2′-biphenol

3,3′,5,5′-Tetramethyl-2,2′-biphenol is a compound of high technical significance, as it exhibits superior properties as building block for ligands in the transition-metal catalysis. However, side reactions and overoxidation are challenging issues in the conventional synthesis of this particular biphenol. Here, an electrochemical method is presented as powerful and sustainable alternative to conventional chemical strategies, which gives good yields up to 51%. Despite using inexpensive and well-available bromide-containing supporting electrolytes, the issue of bromination and general byproduct formation is effectively suppressed by adding water to the electrolyte. Additionally, the scalabilit…

ChemInform Abstract: Electrochemical Allylic Oxidation of Olefins: Sustainable and Safe

The power you're supplying: With the application of an optimized electrochemical approach, the allylic oxidation of olefins, which is an important C-H activation process that provides access to enones, becomes a sustainable, versatile, and potent key reaction for organic synthesis.

Practical strategies for stable operation of HFF-QCM in continuous air flow

Currently there are a few fields of application using quartz crystal microbalances (QCM). Because of environmental conditions and insufficient resolution of the microbalance, chemical sensing of volatile organic compounds in an open system was as yet not possible. In this study we present strategies on how to use 195 MHz fundamental quartz resonators for a mobile sensor platform to detect airborne analytes. Commonly the use of devices with a resonant frequency of about 10 MHz is standard. By increasing the frequency to 195 MHz the frequency shift increases by a factor of almost 400. Unfortunately, such kinds of quartz crystals tend to exhibit some challenges to obtain a reasonable signal-to…

Azolylborates for Electrochemical Double Layer Capacitor Electrolytes

Abstract Asymmetric tetraalkylammonium salts of azolylborates were synthesized and studied with respect to their suitability as supporting electrolytes in electrochemical double layer capacitors. In contrast to current conducting salts used in this device, azolylborates exhibit an excellent stability towards thermal load and moisture. In addition to good conductivity and stability towards cathodic reduction we found certain limitations when more positive potentials were applied.

Crystal structure of 12-benzylsulfanyl-2,9-dibromo-6H-dibenzo[b,g][1,8]naphthyridin-11-one

The hetero-tetra-cene skeleton of the title mol-ecule, C23H14Br2N2OS, is defined by linear annulation of four six-membered rings, including two N heteroatoms. This moiety is nearly planar (r.m.s. deviation = 0.055 Å), with a slight twist of 4.1 (2)° between the two halves of the aromatic system. The dihedral angle between the least-squares plane of the skeleton and the benzyl group is 24.5 (3)°; the C-S-C angle involving the benzyl-sulfanyl group is 99.2 (4)°. In the crystal, mol-ecules are π-stacked in an anti-parallel fashion along [110], with a distance between the aromatic planes of 3.47 (2) Å. Inter-molecular N-H⋯O hydrogen bonds form chains extending parallel to [001] and bridge the a…

Supporting-Electrolyte-Free and Scalable Flow Process for the Electrochemical Synthesis of 3,3′,5,5′-Tetramethyl-2,2′-biphenol

The most efficient electrochemical synthesis of 3,3′,5,5′-tetramethyl-2,2′-biphenol by dehydrogenative coupling is reported. The electrolysis is performed supporting-electrolyte-free in 1,1,1,3,3,3...

Direct gravimetric sensing of GBL by a molecular recognition process in organic cage compounds.

Organic cages were identified as highly potent affinity materials for the tracing of γ-butyrolactone. The selectivity over ethanol and water is based on the interior functional groups which allow preferential hydrogen bonding to the target analyte.

Electrosynthesis of 3,3′,5,5’-tetramethyl-2,2′-biphenol in flow

Abstract3,3′,5,5’-Tetramethyl-2,2′-biphenol is well known as an outstanding building block for ligands in transition-metal catalysis and is therefore of particular industrial interest. The electro-organic method is a powerful, sustainable, and efficient alternative to conventional synthetic approaches to obtain symmetric and non-symmetric biphenols. Here, we report the successive scale-up of the dehydrogenative anodic homocoupling of 2,4-dimethylphenol (4) from laboratory scale to the technically relevant scale in highly modular narrow gap flow electrolysis cells. The electrosynthesis was optimized in a manner that allows it to be easily adopted to different scales such as laboratory, semit…

Initial Radical Cation Pathway in the Mo2Cl10-Mediated Dehydrogenative Arene Coupling

Experimental (EPR) and theoretical (DFT) evidence is provided for radical cation formation as initial step in the Mo2Cl10-mediated dehydrogenative arene coupling. The initial electron transfer from methoxyarenes to molybdenum proceeds via an inner sphere mechanism.

CCDC 1831234: Experimental Crystal Structure Determination

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CCDC 1485994: Experimental Crystal Structure Determination

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CCDC 966732: Experimental Crystal Structure Determination

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CCDC 1415863: Experimental Crystal Structure Determination

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CCDC 1040031: Experimental Crystal Structure Determination

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CCDC 1520081: Experimental Crystal Structure Determination

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CCDC 1840041: Experimental Crystal Structure Determination

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CCDC 2070594: Experimental Crystal Structure Determination

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CCDC 1429063: Experimental Crystal Structure Determination

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CCDC 1569308: Experimental Crystal Structure Determination

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CCDC 980571: Experimental Crystal Structure Determination

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CCDC 1517624: Experimental Crystal Structure Determination

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CCDC 1866675: Experimental Crystal Structure Determination

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CCDC 1961176: Experimental Crystal Structure Determination

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CCDC 1047644: Experimental Crystal Structure Determination

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CCDC 1551854: Experimental Crystal Structure Determination

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CCDC 1476308: Experimental Crystal Structure Determination

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CCDC 1545585: Experimental Crystal Structure Determination

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CCDC 1520080: Experimental Crystal Structure Determination

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CCDC 1920411: Experimental Crystal Structure Determination

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CCDC 1891216: Experimental Crystal Structure Determination

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CCDC 1567670: Experimental Crystal Structure Determination

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CCDC 1567667: Experimental Crystal Structure Determination

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CCDC 980570: Experimental Crystal Structure Determination

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CCDC 1567665: Experimental Crystal Structure Determination

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CCDC 1882077: Experimental Crystal Structure Determination

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CCDC 1894341: Experimental Crystal Structure Determination

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CCDC 980563: Experimental Crystal Structure Determination

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CCDC 1520078: Experimental Crystal Structure Determination

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CCDC 980565: Experimental Crystal Structure Determination

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CCDC 1551855: Experimental Crystal Structure Determination

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CCDC 1979131: Experimental Crystal Structure Determination

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CCDC 1047645: Experimental Crystal Structure Determination

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CCDC 966311: Experimental Crystal Structure Determination

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CCDC 1485996: Experimental Crystal Structure Determination

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CCDC 1520082: Experimental Crystal Structure Determination

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CCDC 1998477: Experimental Crystal Structure Determination

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CCDC 2032478: Experimental Crystal Structure Determination

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CCDC 1998478: Experimental Crystal Structure Determination

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CCDC 1039421: Experimental Crystal Structure Determination

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CCDC 1542681: Experimental Crystal Structure Determination

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CCDC 1039422: Experimental Crystal Structure Determination

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CCDC 1903303: Experimental Crystal Structure Determination

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CCDC 1872281: Experimental Crystal Structure Determination

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CCDC 1998475: Experimental Crystal Structure Determination

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CCDC 980569: Experimental Crystal Structure Determination

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CCDC 1899693: Experimental Crystal Structure Determination

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CCDC 1858697: Experimental Crystal Structure Determination

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CCDC 1589070: Experimental Crystal Structure Determination

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CCDC 804368: Experimental Crystal Structure Determination

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CCDC 1882075: Experimental Crystal Structure Determination

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CCDC 1897052: Experimental Crystal Structure Determination

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CCDC 1476309: Experimental Crystal Structure Determination

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CCDC 1517625: Experimental Crystal Structure Determination

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CCDC 1415860: Experimental Crystal Structure Determination

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CCDC 1415861: Experimental Crystal Structure Determination

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CCDC 1998476: Experimental Crystal Structure Determination

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CCDC 980564: Experimental Crystal Structure Determination

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CCDC 1025809: Experimental Crystal Structure Determination

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CCDC 1894340: Experimental Crystal Structure Determination

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CCDC 1920412: Experimental Crystal Structure Determination

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CCDC 1567666: Experimental Crystal Structure Determination

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CCDC 1561793: Experimental Crystal Structure Determination

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CCDC 980568: Experimental Crystal Structure Determination

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CCDC 1882076: Experimental Crystal Structure Determination

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CCDC 1427184: Experimental Crystal Structure Determination

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CCDC 1008816: Experimental Crystal Structure Determination

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CCDC 1988067: Experimental Crystal Structure Determination

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CCDC 1008819: Experimental Crystal Structure Determination

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CCDC 1542680: Experimental Crystal Structure Determination

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CCDC 1561794: Experimental Crystal Structure Determination

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CCDC 1882073: Experimental Crystal Structure Determination

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CCDC 1831233: Experimental Crystal Structure Determination

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CCDC 1561792: Experimental Crystal Structure Determination

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CCDC 1961177: Experimental Crystal Structure Determination

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CCDC 1841752: Experimental Crystal Structure Determination

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CCDC 1485995: Experimental Crystal Structure Determination

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CCDC 1846985: Experimental Crystal Structure Determination

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CCDC 1945339: Experimental Crystal Structure Determination

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CCDC 1008820: Experimental Crystal Structure Determination

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CCDC 1047647: Experimental Crystal Structure Determination

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CCDC 942549: Experimental Crystal Structure Determination

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CCDC 1846986: Experimental Crystal Structure Determination

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CCDC 1988057: Experimental Crystal Structure Determination

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CCDC 980566: Experimental Crystal Structure Determination

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CCDC 1896228: Experimental Crystal Structure Determination

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CCDC 1891217: Experimental Crystal Structure Determination

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CCDC 1920410: Experimental Crystal Structure Determination

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CCDC 1567668: Experimental Crystal Structure Determination

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CCDC 1894339: Experimental Crystal Structure Determination

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CCDC 1831232: Experimental Crystal Structure Determination

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CCDC 1567669: Experimental Crystal Structure Determination

Related Article: Jana Marie Stahlhofen, Dieter Schollmeyer, Siegfried R. Waldvogel|2017|Eur.J.Org.Chem.|2017|7226|doi:10.1002/ejoc.201701124

CCDC 1976461: Experimental Crystal Structure Determination

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CCDC 1897051: Experimental Crystal Structure Determination

Related Article: Ephraim Prantl, Bernd Kohl, Dimitrij Ryvlin, Philipp Biegger, Hubert Wadepohl, Frank Rominger, Uwe H. F. Bunz, Michael Mastalerz, Siegfried R. Waldvogel|2019|ChemPlusChem|84|1239|doi:10.1002/cplu.201900189

CCDC 1831236: Experimental Crystal Structure Determination

Related Article: Alexander Lipp, Dorota Ferenc, Christoph Gütz, Mario Geffe, Nina Vierengel, Dieter Schollmeyer, Hans J. Schäfer, Siegfried R. Waldvogel, Till Opatz|2018|Angew.Chem.,Int.Ed.|57|11055|doi:10.1002/anie.201803887

CCDC 1589072: Experimental Crystal Structure Determination

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CCDC 1569307: Experimental Crystal Structure Determination

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