Alcohol/Water-Relay Sulfurative Oxygenation of Vinyl Bromides Enabled by Photoinduced EDA Complexes

The direct conversion of vinyl halides into oxygenated sulfur-containing carbonyl compounds using water as the oxygen source remains challenging because it requires coordinated C-halogen activation, radical capture, oxygen incorporation, and C-S bond formation under mild conditions. Here we report a photoinduced electron donor-acceptor complex strategy that enables the sulfurative oxygenation of vinyl bromides with thiols in an EtOH/H2O medium under metal- and oxidant-free conditions. In this process, thiolate formation triggers EDA complex assembly with vinyl bromides, and light excitation initiates C-Br fragmentation to generate a styrenyl radical that is intercepted through an alcohol/water relay. The reaction provides α-thioaryl ketones in up to 81% yield across 32 examples and can be performed on a gram scale. Mechanistic experiments, including radical trapping, EPR, H218O labeling, UV-vis spectroscopy, NMR titration, cyclic voltammetry, and DFT calculations, support a radical-polar pathway involving ethanol trapping, water addition, sulfur transfer, and tautomerization.