A new functionalized, chiral disulfide derived from l-cysteine: (R,R)-bis[(3-benzyloxazolan-4-yl)-methane] disulfide as a catalyst in the diethylzinc addition to aldehydes
作者:Antonio L Braga、Helmoz R Appelt、Paulo H Schneider、Claudio C Silveira、Ludger A Wessjohann
DOI:10.1016/s0957-4166(99)00145-7
日期:1999.5
A new, easily accessible, chiral disulfide 3 was prepared from L-cysteine in a short synthetic sequence (Scheme 1) and applied successfully as a highly efficient catalyst for the enantioselective addition of diethyl zinc to aromatic and aliphatic aldehydes to afford the product alcohols in up to more than 99% ee. In contrast to the more common amino alcohols used in similar reactions, catalyst 3 does not have a protic hydrogen in the form of a free hydroxy group. (C) 1999 Elsevier Science Ltd. All rights reserved.
New C 2 -symmetric chiral disulfide ligands derived from ( R )-cysteine
作者:Antonio L Braga、Helmoz R Appelt、Paulo H Schneider、Oscar E.D Rodrigues、Claudio C Silveira、Ludger A Wessjohann
DOI:10.1016/s0040-4020(01)00199-5
日期:2001.4
Several sulfur-containing optically active C2-symmetrical ligands have been synthesized from (R)-cysteine and applied successfully as chiral catalysts in the asymmetric addition of diethylzinc to aldehydes. The resulting secondary alcohols could be obtained in good yields and excellent enantiomeric excess.
First Generation Cysteine- and Methionine-Derived Oxazolidine and Thiazolidine Ligands for Palladium-Catalyzed Asymmetric Allylations
作者:Paulo H. Schneider、Henri S. Schrekker、Claudio C. Silveira、Ludger A. Wessjohann、Antonio L. Braga
DOI:10.1002/ejoc.200300675
日期:2004.6
series of enantiopure oxazolidine-thioether and thiazolidine-alcohol ligands have been synthesized from L-cysteine, S-methyl-L-cysteine, and L-methionine in a straightforward manner that allows numerous structural variations to be formed. These types of ligands have not previously been used in asymmetricpalladium-catalyzedallylations and their efficacy was explored in the reaction of rac-1,3-diphenyl-2-propenyl