Screening of ligands in the asymmetric metallocenethiolatocopper(I)-catalyzed allylic substitution with Grignard reagents
作者:Hanna K. Cotton、Jakob Norinder、Jan-E. Bäckvall
DOI:10.1016/j.tet.2006.03.100
日期:2006.6
Screening of metallocenethiolate ligands for copper(I)-catalyzed substitution of allylic acetates with Grignardreagents has been carried out. The previously used ligand, lithium (R,Sp)-2-(1-dimethylaminoethyl)ferrocenylthiolate (4a), possessing both central and planar chirality, was the starting point for the screening. It was found that the diastereomeric ligand lithium (R,Rp)-2-(1-dimethylamino
dimethylphenylsilylmethylmagnesium chloride result in highly regioselective dehydrohalogenation. The reaction does not follow the conventional E2 elimination mechanism but includes beta-hydride elimination from the corresponding alkylcobalt intermediate. The interesting reaction mechanism of the cobalt-catalyzed dehydrohalogenation offered unique transformations that are otherwise difficult to attain.
Enantioselective Copper-Mediated Allylic Substitution with Grignard Reagents Employing a Chiral Reagent-Directing Leaving Group
作者:Bernhard Breit、Daniel Breuninger
DOI:10.1055/s-2004-831247
日期:——
Enantioselective copper-mediated allylic substitution with Grignard reagents was achieved employing the ortho-diphenylphosphanylferrocene carboxylate (o-DPPF) system as a planar chiral reagent-directing leaving group. Careful optimization of reaction parameters resulted in excellent regioselectivities and enantioselectivies of up to 95% ee.
利用邻二苯基膦酰二茂铁羧酸酯(邻DPPF)体系作为平面手性试剂导向离去基团,实现了铜介导的烯丙基取代格氏试剂的对映体选择性。通过对反应参数的精心优化,获得了极佳的区域选择性和高达 95% ee 的对映选择性。
Allylic chlorides and phosphates reacted with alkyl-Grignard reagent in an S(N)2'-selective manner in the presence of a catalytic amount of 1,2,3-triazol-5-ylidenes to provide a-branched alkenes. (C) 2013 Elsevier Ltd. All rights reserved.