Asymmetric Visible-Light Photoredox Cross-Dehydrogenative Coupling of Aldehydes with Xanthenes

We report a methodology for the catalytic asymmetric cross-coupling of two C­(sp3)–H bonds employing visible light as an economical and environmentally benign source of energy. Photoredox catalysis is used for the oxidation of a diarylmethane to the corresponding cation, which is then trapped by an enamine intermediate generated in situ from an aldehyde reactant and a secondary amine organocatalyst. Notably, this mild method is an ideal synthetic approach from the green chemistry point of view. It does not require preinstallation of functional groups, thereby constituting an atom economical, efficient transformation, and it allows the formation of a C–C bond with simultaneous installation of one or two new stereocenters in a highly enantio- and diastereoselective manner. Mechanistic studies by experimental and computational methods aid to clarify the origin of the observed enantioselectivity.