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

Direct allylic C-H thiolation is straightforward for allylic C(sp(3))-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(sp(3))-H thiolation has proved difficult. Represented herein is an exceptional for direct, efficient, atom- and step-economic thiolation of allylic C(sp(3))-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 (H-2) is produced as byproduct. When vinylic C(sp(2))-H was used instead of allylic C(sp(3))-H bond, the radical-radical cross-coupling of C(sp(2))-H and S-H was achieved with liberation of H-2. Such a unique transformation opens up a door toward direct C-H and S-H coupling for valuable organosulfur chemistry.

Automated summary

An efficient, atom- and step-economic method for direct allylic C(sp(3))-H thiolation under visible light irradiation is developed in this study, which does not require external oxidants and radical initiators, with hydrogen produced as a byproduct. Radical trapping experiments showed the involvement of allylic radical and thiyl radical in C-S bond formation on the surface of photocatalyst quantum dots.