Photoinduced C-S Coupling Reaction of Alkenylsulfonium Salts with Thiols in Water.

Alkenyl sulfides are versatile building blocks in organic synthesis, materials science, and pharmaceutical chemistry, yet their preparation often relies on transition-metal catalysis, organic solvents, or photosensitizers. Herein, we report a visible-light-induced C-S coupling of alkenylsulfonium salts with thiols in water without any photosensitizer, metal catalyst, or base. The protocol tolerates diverse thiols and alkenylsulfonium salts, affording alkenyl sulfides in moderated to good yields. The use of dithiols enables sequential double C-S bond formation to provide a one-pot route to cyclic thioacetals. Mechanistic studies implicate an electron donor-acceptor complex, wherein hydrogen-bonding interactions with water play a crucial role.