Enantioselective [2 + 2] photocycloaddition of quinolone using a C 1 -symmetric chiral phosphoric acid as a visible-light photocatalyst.

The enantioselective intra- and intermolecular [2 + 2] photocycloaddition of quinolone using a C 1 -symmetric chiral phosphoric acid as a visible-light photocatalyst is developed. The thioxanthone chromophore on phosphoric acid plays an important role in both phototransformation and enantioselectivity.