Construction of axial chirality via asymmetric radical trapping by cobalt under visible light

Abstract 3d-Metals have been identified as economic and sustainable alternatives to palladium, the frequently used metal in transition-metal-catalyzed cross-couplings. However, cobalt has long stood behind its neighboring elements, nickel and copper, in asymmetric radical couplings, owing to its high catalytic activity in the absence of ligands. Here, we disclose an asymmetric metallaphotoredox catalysis (AMPC) strategy for the dynamic kinetic resolution (DKR) of racemic heterobiaryls, which represents the first example of visible-light-induced, asymmetric radical couplings for the construction of axial chirality. This success can also be extended to the reductive cross-coupling variant featuring on more easily available feedstocks. The keys to these successes are the rational design of a sustainable AMPC system by merging asymmetric cobalt catalysis with organic photoredox catalysis and, perhaps more importantly, the identification of an efficient chiral polydentate ligand.