Photocatalytic Site-Selective Addition of Carbazole C( sp 2 )–H Bonds to Aroylformates: Synthesis of α-Quaternary α-Hydroxyesters

The rapid advancement of organophotochemistry has established radical-mediated nucleophilic addition as a prominent strategy for carbonyl functionalization. Nevertheless, the direct addition of aryl C( sp 2 )–H bonds to carbonyl groups via the radical process remains largely unexplored. Herein, we report a visible-light-driven site-selective addition of carbazole C( sp 2 )–H bonds to aroylformates, which leads to the synthesis of a series of α-quaternary α-hydroxyesters bearing a carbazole scaffold in generally high yields. Mechanistic investigation revealed that the reaction is initiated with reductive quenching of the excited photocatalyst by carbazole and proceeds via a radical–radical cross-coupling process.