α-Heteroarylation of Thioethers via Photoredox and Weak Brønsted Base Catalysis.

We report the C-H activation of thioethers to α-thio alkyl radicals and their addition to N -methoxyheteroarenium salts for the redox-neutral synthesis of α-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 α-C-H deprotonation by a weak Brønsted base catalyst to afford α-thio alkyl radicals. Further, N -methoxyheteroarenium salts play additional roles as a source of methoxyl radical that contributes to α-thio alkyl radical generation and a sacrificial oxidant that regenerates the photoredox catalytic cycle.