Kinetic Resolution of Chiral Cyclohex-2-enones by Rhodium(I)/binap-Catalyzed 1,2- and 1,4-Additions

The feasibility of kinetic resolutions of racemic monosubstituted cyclohex-2-enones by Rh/binap-catalyzed reactions was investigated. 1,2-Addition of AlMe3 to the 5-substituted derivatives furnished allylic alcohols in the matched case, while the less reactive enantiomers were either left over or transformed into trans-3,5-disubstituted cyclohexanones in parallel or sequential 1,4-additions. Altogether, these represent regiodivergent reactions on racemic mixtures. In contrast, 1,4-addition of aryl groups led to inferior results since either catalyst or substrate control dominated.

本研究考察了铑/BINAP（Rh/binap）催化体系对外消旋单取代环己-2-烯酮的动力学拆分（kinetic resolution）可行性。针对5位取代的衍生物，三甲基铝（AlMe3）的1,2-加成在构型匹配的反应条件下可生成烯丙醇；而反应活性较低的对映异构体要么未发生反应，要么通过平行或串联的1,4-加成反应转化为反式-3,5-二取代环己酮。综上，该类反应对外消旋底物混合物实现了区域发散性转化（regiodivergent reactions）。与之相对，芳基的1,4-加成反应效果欠佳，此时反应的立体选择性由催化剂控制或底物控制主导。