Direct Allylic C(sp³)–H Thiolation with Disulfides via Visible Light Photoredox Catalysis

Abstract

In spite of the wide utility of allyl thioethers, the direct catalytic allylic C(sp3)–H thiolation remains elusive. Herein, we report the direct allylic C(sp3)–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(sp3)–H bond followed by C(sp3)–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.