Direct Allylic C(sp3 )-H and Vinylic C(sp2 )-H Thiolation with Hydrogen Evolution by Quantum Dots and Visible Light.

ABSTRACT

Direct allylic C-H thiolation is straightforward for allylic C(sp3 )-S bond formation. However, strong interactions between thiol and transition metal catalysts lead to deactivation of the catalytic cycle or oxidation of sulfur atom under oxidative condition. Thus, direct allylic C(sp3 )-H thiolation has proved difficult. Represented herein is an exceptional for direct, efficient, atom- and step-economic thiolation of allylic C(sp3 )-H and thiol S-H under visible light irradiation. Radical trapping experiments and electron paramagnetic resonance (EPR) spectroscopy identified the allylic radical and thiyl radical generated on the surface of photocatalyst quantum dots (QDs). The C-S bond formation does not require external oxidants and radical initiators, and hydrogen (H2 ) is produced as byproduct. When vinylic C(sp2 )-H was used instead of allylic C(sp3 )-H bond, the radical-radical cross-coupling of C(sp2 )-H and S-H was achieved with liberation of H2 . Such a unique transformation opens up a door toward direct C-H and S-H coupling for valuable organosulfur chemistry.