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.

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...

Self-Sorting Effects in the Self-Assembly of Metallosupramolecular Rhombi from Chiral BINOL-Derived Bis(pyridine) Ligands

Four BINOL-based bis(4-pyridyl) ligands were synthesised in enantiopure and racemic form. These ligands form metallosupramolecular [(dppp)2M2L2] rhombi with cis-protected [(dppp)Pd]2+ and [(dppp)Pt]2+ ions. In principle, racemic ligands can self-assemble into three stereoisomeric rhombi. The degree of self-sorting in the self-assembly process crucially depends on the substitution pattern and the resulting bend angle of the V-shaped ligands as well as the degree of steric crowding within the assembly when racemic ligands are used. Thus, these processes either lead to homochiral assemblies in a narcissistic self-recognition manner, to heterochiral assemblies in a social self-discriminating ma…

A New Structural Motif for an Enantiomerically Pure Metallosupramolecular Pd4L8Aggregate by Anion Templating

An enantiomerically pure BINOL-based bis(3-pyridyl) ligand 1 assembles into a homochiral [Pd4(1)8] complex upon coordination to tetravalent PdII ions. The formation of this aggregate is templated by two tetrafluoroborate counterions that are encapsulated in two peripheral cavities. The resulting structure is a new structural motif for this kind of metallosupramolecular assemblies that arranges the palladium ions in a distorted tetrahedral fashion and forces ligand 1 to adopt two different conformations. Both phenomena are unique and cause an overall three-dimensional structure that has another confined, chiral, and hydrophilic central cavity.

Enantiomerenreine [M6L12]- oder [M12L24]-Polyeder aus flexiblen Bis(pyridin)-Liganden

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

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

Enantiomerically pure [M(6)L(12)] or [M(12)L(24)] polyhedra from flexible bis(pyridine) ligands.

Coordination-driven self-assembly is one of the most powerful strategies to prepare nanometer-sized discrete (supra)molecular assemblies. Herein, we report on the use of two constitutionally isomeric BINOL-based bis(pyridine) ligands for this purpose. Upon coordination to Pd(II) ions these self-assemble into enantiomerically pure endo- and exo-functionalized hexa- and dodecanuclear metallosupramolecular spheres with a chiral skeleton depending on the substitution pattern of the BINOL core. These aggregates were characterized by NMR, MS, DLS, TEM, and EELS as well as ECD. Furthermore, experimental ECD data could be compared to those obtained from theoretical simulations using a simplified Ta…

Enantiomerically pure trinuclear helicates via diastereoselective self-assembly and characterization of their redox chemistry.

A tris(bipyridine) ligand 1 with two BINOL (BINOL = 2, 2′-dihydroxy-1, 1′-binaphthyl) groups has been prepared in two enantiomerically pure forms. This ligand undergoes completely diastereoselective self-assembly into D2-symmeteric double-stranded trinuclear helicates upon coordination to copper(I) and silver(I) ions and to D3-symmetric triple-stranded trinuclear helicates upon coordination to copper(II), zinc(II), and iron(II) ions as demonstrated by mass spectrometry, NMR and CD spectroscopy in combination with quantum chemical calculations and X-ray diffraction analysis. According to the calculations, the single diastereomers that are formed during the self-assembly process are strongly …

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…

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

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.

Leaded Bronze: An Innovative Lead Substitute for Cathodic Electrosynthesis

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)

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.

Ein enantiomerenreines metallosupramolekulares Pd4L8-Aggregat mit neuartigem Strukturmotiv: Bildung durch einen Anionen-Templateffekt

Ein enantiomerenreiner Bis(3-pyridyl)-Ligand 1 auf der Basis eines BINOL-Gerusts bildet mit tetravalenten PdII-Ionen einen homochiralen [Pd4(1)8]-Komplex. Zwei Tetrafluoroborationen dienen dabei als Template fur die Bildung dieses Aggegates und werden in zwei periphere Kavitaten eingeschlossen. Die dadurch resultierende Struktur reprasentiert ein neues Strukturmotiv fur diese Sorte von metallosupramolekularen Assemblaten, in dem die vier Palladiumionen in einer verzerrt tetraedrischen Anordnung zu finden sind. Dies zwingt den Liganden 1, zwei verschiedene Konformationen in dem Aggregat einzunehmen. Beide Phanomene sind einzigartig und fuhren uberdies zur Bildung einer dreidimensionalen Stru…

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…

CCDC 1831234: Experimental Crystal Structure Determination

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CCDC 945021: Experimental Crystal Structure Determination

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CCDC 945019: Experimental Crystal Structure Determination

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CCDC 1003004: Experimental Crystal Structure Determination

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CCDC 1831233: Experimental Crystal Structure Determination

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CCDC 1831232: Experimental Crystal Structure Determination

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CCDC 941094: Experimental Crystal Structure Determination

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CCDC 1831236: Experimental Crystal Structure Determination

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CCDC 945020: Experimental Crystal Structure Determination

Related Article: Christoph Gütz, Rainer Hovorka, Caroline Stobe, Niklas Struch, Filip Topić, Gregor Schnakenburg, Kari Rissanen, Arne Lützen|2014|Eur.J.Org.Chem.|2014|206|doi:10.1002/ejoc.201301314

CCDC 941095: Experimental Crystal Structure Determination

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CCDC 1831235: Experimental Crystal Structure Determination

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CCDC 982088: Experimental Crystal Structure Determination

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