Chromones as Photocatalyzed HAT Reagent and Michael Acceptor for Direct C-H Alkylation of 2-Substituted 4-Chromanones

4-Chromanone is a biologically important heterocyclic scaffold found in natural products and pharmaceuticals. Traditional syntheses of 2-substituted 4-chromanones often rely on high-temperature peroxide initiation, transition-metal catalysis, or complex photocatalytic systems, limiting functional-group tolerance and sustainability. Herein, we report a Giese-type strategy for direct C-H functionalization of chromone derivatives, where chromones act as both substrates and hydrogen atom transfer (HAT) reagents to active inert C(sp³)-H bonds and P-H bonds under mild, metal-free conditions. Upon light irradiation, chromones form triplet states that mediate HAT for diverse substrates, including ethers, esters, alcohols, alkanes, sulfides, and arylphosphines. The resulting radicals are captured by ground-state chromones, efficiently affording 2-substituted 4-chromanones. Mechanistic studies and density functional theory calculations support the radical-mediated pathway, and the method avoids the use of metal catalysts, external redox mediators, or photocatalysts, highlighting its scalability and sustainable potential.