Acceleration of Enantioselective Cycloadditions Catalyzed by Second-Generation Chiral Oxazaborolidinium Triflimidates by Biscoordinating Lewis Acids
作者:Barla Thirupathi、Simon Breitler、Karla Mahender Reddy、E. J. Corey
DOI:10.1021/jacs.6b08018
日期:2016.8.31
oxazaborolidines by the strong acid triflimide (Tf2NH) in CH2Cl2 solution leads to highly active chiralLewis acids that are very effective catalysts for (4 + 2) cycloaddition. We report herein that this catalytic activity can be further enhanced by the use of Tf2NH in combination with the biscoordinating Lewis acid TiCl4 or SnCl4 as a coactivator. The effective increase in acidity of an exceedingly strong
SuperQuat 5,5-dimethyl-4-iso-propyloxazolidin-2-one as a mimic of Evans 4-tert-butyloxazolidin-2-one
作者:Steven D. Bull、Stephen G. Davies、A. Christopher Garner、Dennis Kruchinin、Min-Suk Key、Paul M. Roberts、Edward D. Savory、Andrew D. Smith、James E. Thomson
DOI:10.1039/b605244d
日期:——
The incorporation of a gem-dimethyl group at the 5-position of a chiral oxazolidinone biases the conformation of the adjacent C(4)-stereodirecting group such that the gem-dimethyl-4-iso-propyl combination mimics a C(4)-tert-butyl group, providing higher levels of stereocontrol than a simple 4-iso-propyloxazolidinone. The generality of this principle is demonstrated with applications in stereoselective enolate alkylations, kinetic resolutions, Diels–Alder cycloadditions and Pd-catalysed asymmetric acetalisation reactions.
Asymmetric Lewis Acid-Catalyzed Diels−Alder Reactions of α,β-Unsaturated Ketones and α,β-Unsaturated Acid Chlorides
作者:Joel M. Hawkins、Mitch Nambu、Stefan Loren
DOI:10.1021/ol035524t
日期:2003.11.1
[reaction: see text] Conformational analysis, van der Waals attractions, and transition structure calculations are combined to design an asymmetric Lewis acid-catalyzed Diels-Alder reaction for simple acyclic alpha,beta-unsaturated ketones and alpha,beta-unsaturated acid chlorides, giving up to 83 and 92% ee, respectively. The two-point-binding chiral recognition mechanism, Lewis acid-Lewis base coordination