Mechanistic understanding of the dual gold and photoredox-catalyzed thiosulfonylation of alkynes and enynes: a DFT study

Abstract

The detailed mechanisms of dual gold and photoredox-catalyzed thiosulfonylation of alkynes and 1,6-enynes with PhSO₂SCF₃ (1) were explored via DFT calculations. Computational results show that the complex Au(I)⋯1 is more ready to undergo a single electron reduction with the excited *[Ru]^II photocatalyst, leading to an Au(I)–SCF₃ intermediate + a benzenesulfonyl radical and an oxidative quenching species [Ru]^III. For the thiosulfonylation of alkynes under dual gold and photoredox catalysis, an Au(I)–Au(II)–Au(III)–Au(I) catalytic cycle could be feasible, which undergoes sequential steps of single electron transfer, radical addition, and reductive elimination, leading to the final product. For the thiosulfonylation of 1,6-enynes, a benzenesulfonyl radical attack on the alkynyl moiety of 1,6-enynes could trigger a subsequent intramolecular cyclization, thus converting an alkenyl radical into an alkyl radical. Whether the aforementioned mechanistic pathway could be applicable to the thiosulfonylation of 1,6-enynes is dependent on steric hindrance. The formation of an Au(III) intermediate via radical addition of the formed alkyl radical might not be feasible when substantial steric hindrance is present. Instead, an atom transfer radical addition process was suggested to lead to the products of thiosulfonylation of 1,6-enynes when the Au(I)–Au(II)–Au(III)–Au(I) catalytic cycle might not be possible. In addition, the origins of substituent-dependent regioselective cyclized difunctionalization products were rationalized.