"Ligand-free" CuI-catalyzed highly efficient intramolecular S-vinylation of thiols with vinyl chlorides and bromides.

With CuI as the catalyst and K(3)PO(4) x 3 H(2)O as the base, highly efficient intramolecular S-vinylation of thiols with vinyl chlorides or bromides was successfully implemented without the help of an additional ligand. Moreover, the competition experiments revealed that the 4-exo cyclization is fundamentally preferred over other modes (5-exo, 6-exo, and 6-endo) of cyclization.