Accessing Thiols Directly from Carboxylic Acids and Elemental Sulfur by Multimodal Acridine Photocatalysis

The thiol group is one of the most biologically important and synthetically versatile organosulfur functionalities that can serve as a central entry point to a wide range of other sulfur-containing functional groups. Despite their cross-disciplinary importance, synthetic access to thiols largely remains dominated by two-electron-mediated processes based on toxic and uneconomical reagents and precursors. We report herein a photocatalytic access to thiols that for the first time merges the structural diversity of carboxylic acids with the ready availability of elemental sulfur, whose radical reactivity is significantly underexplored. The two-phase radical process is facilitated by a multimodal catalytic reactivity of acridine photocatalysis that enables both the PCET-mediated decarboxylative carbon–sulfur bond formation and the previously unknown radical reductive disulfur bond cleavage by a photoinduced HAT process in the silane–acridine system.