Visible-Light-Driven Enantioselective Free Radical Addition to Aldimines via Direct C-H Functionalization.

Enantioselective radical addition to imines provides a powerful approach to access optically active amines under mild conditions. Despite significant advances, most catalytic asymmetric reactions rely on radical precursors bearing directing groups to achieve high levels of stereocontrol. We disclose herein a chiral phosphoric acid-catalyzed, visible-light-driven enantioselective radical addition to imines by direct benzylic C-H functionalization, enabling the use of simple aromatic solvents as radical precursors without preinstalled directing groups. The protocol furnishes a broad range of chiral amines in good yields with enantioselectivities of up to 93% ee. Mechanistic investigations revealed a pathway involving hydrogen atom transfer mediated by an iminium radical cation intermediate generated through photooxidation. This strategy expands the scope of asymmetric photoredox catalysis for direct C-H functionalization and provides a general platform for enantioselective radical addition to imines without directing groups.