Cobalt-Catalyzed Asymmetric Sequential Hydroboration/Isomerization/Hydroboration of 2-Aryl Vinylcyclopropanes

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-(sp3)-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.

Automated summary

A cobalt-catalyzed asymmetric sequential hydroboration/isomerization/hydroboration reaction of 2-aryl vinylcyclopropanes was reported for the first time, yielding valuable chiral 1,5-bis(boronates) with good yields and excellent enantioselectivity. The reaction protocol was successfully applied for the synthesis of (-)-preclamol and chiral 1,2,5-triaryl alkanes.