Light-Promoted Palladium-Catalyzed Regiodivergent Transfer Hydrothiocarbonylation of Alkynes Regulated by Coordinating Anions.

α,β-Unsaturated thioesters are fundamental building blocks in organic synthesis, but their efficient and regioselective construction remains a significant challenge. Traditional palladium-catalyzed carbonylations of alkynes typically require hazardous high-pressure carbon monoxide (CO) and suffer from poor regiocontrol, largely due to catalyst poisoning by CO. To address these limitations, we have developed a visible-light-driven palladium-catalyzed protocol that employs thioformates as safe, bench-stable surrogates under ambient, CO-gas-free conditions. This mild system operates at room temperature without the need for exogenous acids or silanes to generate the key Pd-H species. Remarkably, the regioselectivity of the transformation can be predictably switched between linear and branched α,β-unsaturated thioesters simply by the presence or absence of iodide ions (I-). This work provides a practical and switchable platform for the synthesis of these valuable motifs.