Optically active nitrile oxides: synthesis and 1,3-dipolar cycloaddition reactions
摘要:
Baker's yeast-promoted reduction of the C=C bond in 2-aryl-1-nitropropenes gave the corresponding optically active (R)-2aryl-1-nitropropanes of high enantiomeric purity (ee > 90%). They were next converted with the aid of the Mukaiyama and Hoshino method into the optically active nitrile oxides, which were made to react in situ with ethyl propiolate, methylvinyl ketone and (R)-I-phenyl-2-(phenylsulfonyl)ethyl acrylate to yield the appropriate, enantiomerically enriched, isoxazoles or 4,5-dihydroisoxazoles as diastereomeric mixtures, respectively. (c) 2007 Elsevier Ltd. All rights reserved.
Readily available hydrogen bond catalysts for the asymmetric transfer hydrogenation of nitroolefins
作者:Jakob F. Schneider、Markus B. Lauber、Vanessa Muhr、Domenic Kratzer、Jan Paradies
DOI:10.1039/c1ob05059a
日期:——
focuses on readily accessible thiourea hydrogen bond catalysts derived from amino acids, whose steric and electronic features are modulated by their degree of substitution at the carbinol carbon center. These catalysts were applied in the asymmetric transfer hydrogenation of nitroolefins furnishing the chiral products in up to 99% yield and 86% enantiomeric excess. The proposed catalyst's mode of action
Building the buildingblocks: A highly enantioselective hydrogenation of β‐aryl‐β‐alkyl disubstituted nitroalkenes 1 has been developed. This method results in enantiomericallypure nitroalkanes 2, which are versatile precursors for chemical synthesis.
octahedral iridium complex, an exceptionally active hydrogen-bond-mediated asymmetric catalyst was developed and its mode of action investigated by crystallography, NMR, computation, kinetic experiments, comparison with a rhodium congener, and reactions in the presence of competing H-bond donors and acceptors. Relying exclusively on weak forces, the enantioselective conjugate reduction of nitroalkenes
Light-Enabled Enantiodivergence: Stereospecific Reduction of Activated Alkenes Using a Single Organocatalyst Enantiomer
作者:Theresa Hostmann、John J. Molloy、Kathrin Bussmann、Ryan Gilmour
DOI:10.1021/acs.orglett.9b04263
日期:2019.12.20
Light-enabled enantiodivergence is demonstrated in which the alkene substrate configuration is manipulated (E → Z) prior to organocatalytic reduction with a chiral thiourea and Hantzsch ester. This allows stereodivergent reduction to be regulated at the substrate level with high fidelity and mitigates the need for a second, enantiomeric catalyst (up to 93:07 and 95:5 er). The synthetic utility of this
novel chiral bisphosphine-thiourea ligand was developed and applied in the highly enantioselective hydrogenation of β,β-disubstitutednitroalkenes (up to 99% yield and 99% ee). With low catalytic loading (0.25 mol %), 98% ee and 98% conversion were obtained. The thiourea group takes on an important role in this catalytic system.