α-Heteroarylation of Thioethers via Photoredox and Weak Bronsted Base Catalysis

We report the C-H activation of thioethers to alpha-thio alkyl radicals and their addition to N-methoxyheteroarenium salts for the redox-neutral synthesis of alpha-heteroaromatic thioethers. Studies are consistent with a two-step activation mechanism, where oxidation of thioethers to sulfide radical cations by a photoredox catalyst is followed by alpha-C-H deprotonation by a weak Bronsted base catalyst to afford alpha-thio alkyl radicals. Further, N-methoxyheteroarenium salts play additional roles as a source of methoxyl radical that contributes to alpha-thio alkyl radical generation and a sacrificial oxidant that regenerates the photoredox catalytic cycle.