Photodriven Sm-Catalyzed Asymmetric Ketyl-Olefin Coupling

SmI2 is a privileged, single-electron reductant employed in the synthesis of diverse products. Though traditionally used in (super)stoichiometric amounts, SmI2 has recently been employed catalytically with viable turnover strategies. Enantioselective reductive cross-coupling reactions mediated by SmI2 are scarce and asymmetric methods that use catalytic quantities of SmI2 are unknown. Herein, we report an enantioselective ketyl-olefin coupling, employing a SmI2-derived catalyst with a widely available chiral pyridine-bis(oxazoline) (PyBOX) ligand and a commercially available Ir photocatalyst. A combination of optical, electrochemical, and computational data reveals that a Sm-stabilized PyBOX radical is the reactive species responsible for initiating the reductive coupling step.