Scope and Mechanistic Analysis of the Enantioselective Synthesis of Allenes by Rhodium-Catalyzed Tandem Ylide Formation/[2,3]-Sigmatropic Rearrangement between Donor/Acceptor Carbenoids and Propargylic Alcohols
作者:Zhanjie Li、Vyacheslav Boyarskikh、Jørn H. Hansen、Jochen Autschbach、Djamaladdin G. Musaev、Huw M. L. Davies
DOI:10.1021/ja3061529
日期:2012.9.19
Rhodium-catalyzed reactions of tertiary propargylic alcohols with methyl aryl- and styryldiazoacetates result in tandem reactions, consisting of oxonium ylide formation followed by [2,3]-sigmatropic rearrangement. This process competes favorably with the standard O-H insertion reaction of carbenoids. The resulting allenes are produced with high enantioselectivity (88-98% ee) when the reaction is catalyzed by the
炔丙基叔醇与甲基芳基乙酸酯和苯乙烯基重氮乙酸酯的铑催化反应导致串联反应,包括氧鎓叶立德形成,然后是 [2,3]-σ 重排。该过程与类卡宾的标准 OH 插入反应相得益彰。当反应由四脯氨酸二铑配合物 Rh(2)(S-DOSP)(4) 催化时,生成的丙二烯具有高对映选择性 (88-98% ee)。当外消旋叔炔丙醇用作底物时,可以进行动力学拆分。在动力学拆分条件下,形成的丙二烯具有良好的非对映选择性和对映选择性(高达6.1:1 dr,88-93% ee),未反应的醇被对映体富集到65-95% ee。计算研究表明,高不对称诱导是通过涉及两点连接的有组织的过渡态获得的:醇氧与类卡宾之间的叶立德形成以及醇与羧酸盐配体的氢键合。2,3-sigmatropic 重排通过 OH 键的初始裂解进行,生成具有紧密开壳单线态、三线态和闭壳单线态电子态的中间体。该中间体将具有显着的双自由基特征,这与供体/受体类卡宾和更高度官能化的炔丙醇有利于