Visible Light Photoredox Activation of Elemental Sulfur for Sustainable Thioester Synthesis

Abstract The direct utilization of elemental sulfur (S8) for the synthesis of value-added organosulfur compounds remains challenging owing to its intrinsic thermodynamic and kinetic stability. Herein, we report a visible-light-driven, transition-metal-free photoredox strategy that enables the direct incorporation of elemental sulfur into thioesters from aryl sulfonium salts and aldehydes. This transformation proceeds under mild conditions and exhibits a broad substrate scope, excellent functional group tolerance, and high chemoselectivity, providing efficient access to diverse thioesters, including structurally complex molecules derived from pharmaceuticals, agrochemicals, and functional materials. Mechanistic investigations reveal that the reaction operates through a radical sulfur-transfer pathway involving sequential single-electron activation of aryl sulfonium salts and elemental sulfur, followed by radical coupling to construct the thioester framework. This study establishes a sustainable platform for harnessing elemental sulfur in visible light photoredox catalysis and expands the synthetic utility of sulfonium salts as versatile radical precursors.