Direct Allylic C(sp(3))-H Thiolation with Disulfides via Visible Light Photoredox Catalysis

Abstract

In spite of the wide utility of allyl thioethers, the direct catalytic allylic C(sp(3))-H thiolation remains elusive. Herein, we report the direct allylic C(sp(3))-H thiolation mediated by visible light photoredox catalysis. The use of in situ-generated thiyl radical from disulfide as a hydrogen atom transfer (HAT) reagent and a coupling partner enabled selective cleavage of the allylic C(sp(3))-H bond followed by C(sp(3))-S bond formation. The undesired hydrothiolation, a prevalent reaction from facile thiyl radical addition to olefins, was prevented by the immediate deprotonation of thiol under basic conditions. A wide range of diaryl disulfides and olefins participated in the reaction, producing allyl thioethers with high efficiency. Mechanistic investigations revealed the participation of the photocatalyst as a redox mediator, which was crucial for the transformation of the allyl radical into the allyl cation and further ionic coupling process. Based on the proposed mechanism, a limitation in the synthesis of alkyl allyl sulfide was solved with a rationally designed more reducible unsymmetrical disulfide, which makes the desired catalytic cycle operative.