An addition reaction of pyridine-tetrafluoro-λ⁶-sulfanylchlorides (Py-SF₄Cl) to alkynes and alkenes providing pyridine-tetrafluoro-λ⁶-sulfanyl-alkenes and pyridine-tetrafluoro-λ⁶-sulfanyl-alkanes is represented. The addition of Py-SF₄Cl occurs spontaneously in the presence of reactants, even in total darkness, but is affected in the presence of light. A series of SF₄-bridged pyridines were efficiently synthesized under a couple of environmentally benign conditions in good to high yields. The spontaneous reaction of Py-SF₄Cl is discussed based on the time-dependent analyses of the reaction in the presence or absence of photo-irradiation, and could proceed via a radical process.