Dual-Stereocontrol Asymmetric Cobalt-Catalyzed Hydroboration of Sterically Hindered Styrenes

An oxazoline aminoisopropylpyridine (OAP) was designed and synthesized for cobalt-catalyzed asymmetric hydroboration of sterically hindered styrenes. A unique dual-stereocontrol phenomenon was observed using a rigid OIP·CoCl2 complex or a flexible OAP with CoCl2 as precatalysts, respectively. The reaction could be easily carried out on a gram scale to afford chiral alkylboronic esters which could be converted into diverse C–X (X = C, N, O) bond cross-coupling products. The mechanistically distinct pathways were proposed on the basis of deuterium experiments.