Photochemical Redox Buffering in Copper-Catalyzed Benzylic C-H Phosphatation

Copper-catalyzed radical-relay reactions provide a powerful tool for selective C-H functionalization, yet their implementation with peroxide-based oxidants is typically constrained by the requirement for excess C-H substrate. Herein, we present a photochemical approach to circumvent this limitation with a Cu/bipyridine catalyst, enabling benzylic C-H phosphatation with a limiting amount of the C-H substrate. Mechanistic analysis reveals that blue-light irradiation facilitates phosphate-to-copper charge transfer. This process reduces resting-state Cu(II) to Cu(I), which subsequently activates the peroxide to form an alkoxyl radical for hydrogen-atom transfer. This "photochemical redox buffering" effect establishes a unique method to maintain catalytic Cu activity in radical-relay manifolds.