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.