Dual Photoredox/Cobalt Catalysis Enabled Regiospecific Markovnikov Hydroboration of Unactivated Mono-, Di-, and Trisubstituted Alkenes.

Abstract

Hydroboration of alkenes constitutes an important synthetic tool to assemble valuable alkylboron molecules. Although various protocols have been developed, the regiospecific Markovnikov reactions of unactivated alkenes, in particular for trisubstituted ones, remain formidable challenges. Here, we report a general method for the Markovnikov hydroboration of unactivated mono-, di- and trisubstituted alkenes enabled by dual photoredox/cobalt catalysis. The reaction proceeds via a photoinduced metal-hydride hydrogen atom transfer of unactivated alkenes followed by a versatile radical borylation process. This strategy is characterized by its Markovnikov selectivity, mild reaction conditions, high catalytic efficiency and broad substrate scope. This method demonstrates a reaction pattern that achieves the hydroboration of unactivated alkenes through the combination of reductive metal-hydride hydrogen atom transfer and radical borylation. Moreover, this catalytic system can also be applied to complex substrates derived from natural products. The mechanism presented is supported by control experiments and density functional theory calculations.