Cobalt‐Catalyzed Asymmetric Sequential Hydroboration/Isomerization/Hydroboration of 2‐Aryl Vinylcyclopropanes
Chen‐Hui Chen, Hongliang Wang, Tongtong Li, Dongpo Lu, Jiajing Li, Xie Zhang, Xin Hong, Zhan Lu
Abstract
Abstract A cobalt‐catalyzed asymmetric sequential hydroboration/isomerization/hydroboration of 2‐aryl vinylcyclopropanes was for the first time reported for the preparation of valuable chiral 1,5‐bis(boronates) in good yields with excellent enantioselectivity via asymmetric sequential isomerization/hydroboration of a trisubstituted alkene intermediate. The reaction was carried out smoothly and this protocol was used for asymmetric syntheses of (−)‐preclamol in gram‐scale. The two primary C ( sp 3) −B bonds in chiral 1,5‐bis(boronates) could be distinguished in iterative Suzuki–Miyaura cross‐coupling reaction, delivering chiral 1,2,5‐triaryl alkanes with excellent enantioselectivity. Based on experimental and computational studies, a cobalt‐hydride species was proposed as the active intermediate in hydroboration, isomerization, and second hydroboration reactions.