Photoelectrocatalytic [4+2] Annulation for S‐Heterocycle Assembly Enabled by Proton‐Coupled Electron Transfer (PCET)

Cross‐dehydrogenative couplings (CDC) present an efficient strategy for the assembly of biorelevant heterocycles, but are thus far largely limited to toxic transition metals and rather harsh reaction conditions. In sharp contrast, we, herein report on a mild photoelectrocatalyzed CDC‐[4+2] annulation enabling the synthesis of functionalized isothiochromenes enabled by a proton‐coupled electron transfer (PCET) strategy. The transformative photoelectrocatalysis obviated toxic transition‐metal, high reaction temperatures, and stoichiometric chemical redox reagents. This approach was characterized by exceedingly mild conditions, ample substrate scope, and a commercially available catalyst. Gram‐scale reactions and a telescoped synthesis route reflected the unique potential in the green synthesis of important S‐heterocycles.