Mechanistic Insight into Stereoselective Carbolithiation
Mechanistic Insight into Stereoselective Carbolithiation
复制标题
DOI：
10.1002/chem.201000814
复制
发表时间：
2011-03-01
影响因子：
4.3
通讯作者：
O'Shea, Donal F.
中科院分区：
文献类型：
--
作者：
Gessner, Viktoria H.;Koller, Stephan G.;O'Shea, Donal F.
本文讨论了 β-甲基苯乙烯不对称碳锂化的机理特征。虽然通常需要官能团的存在才能在碳锂化反应中获得高对映选择性，但简单的β-甲基苯乙烯也在(-)-金雀花碱介导的烷基锂化合物加成中提供高选择性。对 β-甲基苯乙烯与 (-)-金雀花碱的碳锂化的计算研究表明，所观察到的选择性是在两种反应物近似时，(-)-金雀花碱.烷基锂加合物和 β-甲基苯乙烯之间非对映异构过渡态排斥效应的结果。相比之下，对于邻氨基β-甲基苯乙烯(E)-苄基(2-丙烯基苯基)胺(4)，中间体氨基锂的X射线结构分析表明了碳锂化机制，其中双键的一侧被酰胺部分屏蔽，仅留下一侧可供手性烷基锂加合物接近。
This article addresses the mechanistic features of asymmetric carbolithiation of beta-methylstyrenes. While often the presence of functional groups is required to obtain high enantioselectivities in carbolithiation reactions, simple beta-methylstyrene also gives high selectivities in (-)-sparteine-mediated addition of alkyl lithium compounds. Computational studies on the carbolithiation of beta-methylstyrene with (-)-sparteine show that the observed selectivities are the result of repulsion effects in the diastereomeric transition states between the (-)-sparteine.alkyl lithium adduct and the beta-methylstyrene, upon approximation of the two reactants. In contrast, for the orthoamino beta-methylstyrene (E)-benzyl(2-propenylphenyl)amine (4) X-ray structure analyses of intermediate lithium amides indicate a carbolithiation mechanism in which one side of the double bond is shielded by the amide moiety, leaving only one side free for approach of the chiral alkyl lithium adduct.