Search results for "Nucleophile"

Titelbild: Measuring the Relative Reactivity of the Carbon–Hydrogen Bonds of Alkanes as Nucleophiles (Angew. Chem. 42/2018)

2018

ChemInform Abstract: Asymmetric Tandem Reactions: New Synthetic Strategies

2010

The use of domino and multicomponent reactions in asymmetric synthesis is con- stantly increasing nowadays. This allows for the synthesis of complex molecules in a single synthetic sequence, usually with high atom economy. Herein, we report three examples of new asymmetric tandem reactions recently developed in our laboratories, giving rise to new families of enantiomerically enriched fluorinated and nonfluorinated heterocycles. Thus, 1,4-dihydropyridines (1,4-DHPs) bearing fluorinated substituents at C6 were assembled by means of a Hantzsch-type reaction; cyclic β-amino carbonyl derivatives were prepared using a cross-metathesis (CM)-intramolecular aza-Michael sequence; while fluorinated i…

The Grignard Reaction − Unraveling a Chemical Puzzle

2020

More than 100 years since its discovery, the mechanism of the Grignard reaction remains unresolved. Ambiguities arise from the concomitant presence of multiple organomagnesium species and the competing mechanisms involving either nucleophilic addition or the formation of radical intermediates. To shed light on this topic, quantum-chemical calculations and ab initio molecular dynamics simulations are used to study the reaction of CH3MgCl in tetrahydrofuran with acetaldehyde and fluorenone as prototypical reagents. All organomagnesium species coexisting in solution due to the Schlenk equilibrium are found to be competent reagents for the nucleophilic pathway. The range of activation energies …

THE KINETICS AND MECHANISM OF THE REACTION OF ONIUM CYCLOPENTADIENYLIDES WITH TETRAHALO-p-BENZOQUINONES

1989

Abstract The reaction of triphenylphosphonium cyclopentadienylide (1) with halogen-substituted p-benzoquinones (4) is shown to give a new class of dipolar (zwitterionic) dyes (5) containing phosphorus. The general structure of these molecules has been investigated by a combination of mass spectrometry and multinuclear (7H, 13C and 31P) nmr using the specialist techniques of DEFT spectroscopy, homonuclear (COSY) and heteronuclear 2-D nmr. In addition, stopped-flow (uv/visible) techniques have been used to study the kinetics of the reactions and hence demonstrate that the rate-limiting step is nucleophilic addition of the ylid nucleophile to the quinone, followed by a rapid loss of halide ion…

Global and local reactivity indices for electrophilic/nucleophilic free radicals

2013

A set of five DFT reactivity indices, namely, the global electrophilicity ω° and nucleophilicity N° indices, the radical Parr function P°k, and the local electrophilicity ω°k and nucleophilicity N°k indices, for the study of free radicals (FRs) are proposed. Global indices have been tested for a series of 32 FRs having electrophilic and/or nucleophilic activations. As expected, no correlation between the proposed global electrophilicity ω° and global nucleophilicity N° has been found. Analysis of the local electrophilicity ω°k and nucleophilicity N°k indices for FRs, together with analysis of the local electrophilicity ωk and nucleophilicity Nk indices for alkenes, allows for an explanation…

Coupling of Azomethine Ylides with Nitrilium Derivatives ofcloso-Decaborate Clusters: A Synthetic and Theoretical Study

2012

The azomethine ylides p-R3C5H4N+CH−COC6H4R2-p (3 a: R3=H, R2=H, X=Br; 3 b: R3=H, R2=Me, X=I; 3 c: R3=H, R2=OMe, X=I; 3 d: R3=H, R2=F, X=I; 3 e: R3=Me, R2=Me, X=Br) react with the nitrile functionality of the closo-decaborate clusters [Bun4N][B10H9(NCR1)] (1 a: R1=Me; 1 b: R1=Et; 1 c: R1=Ph) in a CH3NO2 solution under mild conditions (20–25 °C, 2 min) to afford selectively products of the nucleophilic addition (ca. quantitative yields based on NMR analysis in [D6]DMSO, 71–87 % yield of isolated products). These products are the borylated enamino ketones as the salts bearing exclusively a tetrabutylammonium cation [Bun4N][B10H9{NCR1=C(N+C5H4R3-p)COC6H4R2-p}] (4 a–h,k–n) or the mixed salts [Bu…

Addition of Nucleophiles to Fluorinated Michael Acceptors

2016

A series of nucleophiles, including primary and secondary amines, primary alcohols, and thiols, as well as diethyl malonate and nitromethane, were added to different fluorinated Michael acceptors including 2-fluoroalk-1-en-3-ones and 2-fluoro-1-phenylprop-2-en-1-one. The resulting beta-substituted afluoro ketones were isolated in 34-92 % yield, depending on the substrate and the nucleophile. The best yields were obtained with secondary amines and with p-methylthiophenol.

1,4-Benzoquinones with Styryl Substituents

2002

2-Styryl-1,4-benzoquinone (1) and compounds 2 and 3 containing 1 as a substructure all proved to be highly reactive towards thermal or photochemical [4π + 2π] cyclodimerization reactions. Chemo-, regio- and stereoselective processes lead to dimers (compounds 1−10), which can undergo secondary reactions consisting of the addition of nucleophiles combined with a twofold keto-enol tautomerism (10 ⇄ 12). An alternative process is dehydrogenation/oxidation followed by an intramolecular [4π + 2π] cycloaddition (10 ⇄ 11). The same selective [4π + 2π] cyclodimerization can be observed in solution upon irradiation (e.g., 1a ⇄ 10a), in contrast to irradiation in the crystalline state which yields a […

A DFT study of the domino reactions between imidazole NHC, ketenimines and DMAD or MP acetylene derivatives yielding spiro-pyrroles

2014

Abstract The domino reactions of imidazole carbene 9, ketenimine 10 and DMAD 5 or MP 7 to yield the formal [3+2] cycloadducts 12 or 14 have been investigated using DFT methods at the B3LYP/6-31G* level. These domino reactions are initialized by the nucleophilic attack of imidazole 9 on ketenimine 10 to yield the zwitterionic intermediate 11. The second reaction is a formal [3+2] cycloaddition (32CA) reaction between the zwitterionic intermediate 11 and acetylene carboxylates DMAD 5 or MP 7 yielding spiro-pyrroles 12 and 14. These formal 32CA reactions are initialized by the nucleophilic attack of the N3 nitrogen of intermediate 11 on the most electrophilic centres of these acetylene derivat…

Synthesis of 1-Palmitoyl-2-((E)-9- and (E)-10-nitrooleoyl)-sn-glycero-3-phosphatidylcholines

2019

Extensive investigation of nitrated phospholipids in connection with various biologically important processes requires reliable access to suitable material. A selective chemical synthesis introducing a defined nitrofatty acid at the sn-2 position of a 2-lyso sn-glycero-3-phosphatidylcholine was developed. Given that the nitroalkene moiety of both reactant nitrofatty acid derivative and the product esters is characterised by particular sensitivity to nucleophile addition and, depending on the intermediate, subsequent olefin isomerisation and retro-Henry-type reaction, a reliable two-step ester formation was introduced. The activation of the nitrofatty acid succeeded after reaction with trich…