Visible-Light-Induced Metal-Free Regioselective C–H α-Carbonyl Alkylation of 4-Aminocoumarins Using 10-Phenylphenothiazine

We report a visible-light-induced photoredox method for the regioselective C3 α-carbonyl alkylation of 4-aminocoumarin derivatives. The protocol avoids transition metals and uses 10-phenylphenothiazine (PTH) as an efficient, inexpensive organic photocatalyst in place of the costly Ir(ppy)3. With α-carbonyl alkyl bromides as radical precursors, the reaction shows a broad substrate scope and delivers a range of C3 α-carbonyl alkylated 4-aminocoumarins in moderate to excellent yields.