Electrochemical Oxidation of C(sp3)–H Bonds for the Construction of C–S Bonds: Access to 9-Thioxanthenes

Radical-radical cross-coupling offers an efficient strategy for constructing C-S bonds, yet existing methods typically rely on stoichiometric oxidants or metal catalysts. The lack of sustainable approaches for C(sp³)-H sulfenylation at the C9 position of xanthene derivatives limits their functionalization. Herein, we developed an electrochemical method enabling direct C(sp³)-H sulfenylation/selenylation of oxa/thia/aza-xanthenes under metal- and chemical-oxidant-free conditions. Using a carbon rod anode, platinum cathode, Et₄NBF₄ electrolyte, and DCM/EtOH solvent at 10 mA constant current, this strategy achieved broad substrate scope, accommodating diverse benzenethiols, allyl mercaptan, and diphenyl diselenide. Gram-scale synthesis demonstrated practical utility, while mechanistic studies confirmed a radical cross-coupling pathway involving disulfide intermediates. This protocol provides an environmentally benign platform for synthesizing 9-thioxanthenes and related chalcogen-functionalized scaffolds.