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

The 3 d metals have been identified as economic and sustainable alternatives to palladium, the frequently used metal in transition-metal-catalysed cross-couplings. However, cobalt has long stood behind its neighbouring elements, nickel and copper, in asymmetric radical couplings owing to its high catalytic activity in the absence of ligands resulting in unfavourable un-asymmetric background reactions. Here we disclose an asymmetric metallaphotoredox catalysis (AMPC) strategy for the dynamic kinetic asymmetric transformation of racemic heterobiaryls, which represents a visible-light-induced, asymmetric radical coupling for the construction of axial chirality. This success can also be extended to the reductive cross-coupling variant featuring the use of more easily available organic halide feedstocks. The keys to these achievements are the rational design of a sustainable AMPC system that merges asymmetric cobalt catalysis with organic photoredox catalysis in combination with the identification of an efficient chiral polydentate ligand. Controlling the enantioselectivity in metallaphotoredox-catalysed radical cross-couplings using cobalt has proven challenging. Now, the identification of a chiral polydentate ligand enables cobalt-catalysed enantioselective couplings with a broad scope of radicals affording chiral heterobiaryl products.