A facile light-driven C-S bond formation. Photosensitized Benzophenone Preparation of Thioethers from Alkenes.

A simple, metal- and oxidant-free photosensitized reaction has been developed to promote the hydrothiolation of olefins using benzophenone as an inexpensive photocatalyst at room temperature. The photoinduced reaction involves an anti-Markovnikov addition of a wide variety of alkyl thiols and thiophenol to an interesting family of activated and, particularly, inactivated alkenes, which are formed in good to excellent yields and with high regioselectivity. The present photosensitized reaction is operationally simple, tolerates a variety of functional groups and proceeds efficiently within 1 h of reaction time. Additional experiments were also carried out to shed some light on the reaction mechanism. The course of the photoreaction was followed by 1H-NMR spectroscopy, was quenched with TEMPO, a known efficient radical trapping, demonstrating that a radical chain process is involved, and the use of deuterated solvents showed a primary isotope effect. On-off mechanistic experiment was also carried out demonstrating that light is a required reagent and the radical intermediate of the photoreaction is quickly quenched when the light is off. Based on these results a plausible reaction mechanism was proposed.