Asymmetric synthesis of unusual amino acids: Synthesis of optically pure isomers of β-methylphenylalanine
作者:Ramalinga Dharanipragada、Ernesto Nicolas、Geza Toth、Victor J. Hruby
DOI:10.1016/s0040-4039(01)93366-0
日期:1989.1
All the four individual isomers of β-methylphenylalanine have been synthesized in very high optical purities by utilizing in part the chiral imide enolate bromination methodology of Evans and co-workers.
Grignard reagents or the Li[RCuI] reagents in ether favor the opposite syn-s-cis conformation. Influence of lithium ions on the stereoselective conjugate addition of the monoorganocuprate reagent, Li[BuCuI], has been investigated and two different mechanistic pathways are presented. The results show that iodotrimethylsilane (TMSI) is crucial for the asymmetric conjugate addition of the copper reagent, but
first palladium-catalyzed diastereoselective conjugate addition of arylboronic acids to chiral imides is reported. The catalytic system employing 4-tert-butyloxazolidin-2-one as the chiral auxiliary in a mixed solvent system of MeOH/H2O (1:3) under an air atmosphere provides the optically active 3-arylbutanoic acid derivatives in excellent yields with high diastereoselectivity.
据报道,芳基硼酸第一次钯催化的非对映选择性共轭加成到手性酰亚胺上。在空气气氛下,在MeOH / H 2 O(1:3)混合溶剂体系中,以4-叔丁基恶唑烷-2-酮为手性助剂的催化体系提供了具有优异收率的旋光性3-芳基丁酸衍生物。高非对映选择性。
Asymmetric conjugate additions of TMSI promoted monoorganocuprate reagents, Li[RCuI], to various N-enoyl oxazolidinones
Diastereoselective conjugate additions to different α,β-unsaturated N-acyl oxazolidinones using various monoorganocuprate reagents, Li[RCuI], are described. The TMSI activated conjugate addition reactions provided high yields (80–98%) and reversed major diastereomers (70–96% de) compared to the conventional copper(I)-promoted additions of Grignardreagents or the addition of Li[RCuI] to precomplexed MgBr2/imides
Diastereoselection in the conjugate additions of organocopper reagents to N-enoyloxazolidinones
作者:David R Williams、William S Kissel、Jie Jack Li
DOI:10.1016/s0040-4039(98)01966-2
日期:1998.11
A survey of conjugate additions of Yamamoto organocopperreagents to N-enoyl-4-substituted oxazolidinones is reported. Diastereofacial selectivity is reversed for 4-phenyl and 4-benzyloxazolidinones of the same relative configuration. Alkenylcopper reagents demonstrate superior results in asymmetric additions using the 4-phenyloxazolidinone auxiliary.