External photocatalyst- and additive-free visible light-driven direct benzylic C–H functionalization with 1,2-diketones

Abstract

The direct functionalization of benzylic C–H bonds represents a significant synthetic challenge. Herein, we disclose a visible light-driven direct benzylic C–H functionalization using 1,2-diketones as both the hydrogen atom transfer (HAT) reagent and the radical coupling partner. This operationally simple method proceeds under exceptionally mild conditions without requiring any external photocatalysts, additional HAT reagents, and additives. The transformation provides direct access to benzyl-substituted tertiary α-hydroxy ketones with excellent functional group tolerance and broad substrate scope. Mechanistic investigations support a pathway involving photoexcited ketone-mediated HAT with alkylarenes to generate ketyl and benzylic radical pairs, which subsequently undergo a radical–radical cross-coupling to form the desired products.