Alkynyl thioethers are versatile intermediates in organic synthesis, and a synthetic strategy involving C-H/S-H oxidative cross-coupling is atom-economical and effective. However, the homocoupling of alkynes is hard to be prevented under aerobic conditions. Herein, we report an oxygen-free electrochemical oxidative coupling of terminal alkynes with thiophenols via an alternating current (AC) electrosynthesis. This approach stabilizes active Cu species and suppresses copper deposition via precisely controlling current, frequency, and duty ratio. The method affords up to 83% yields without external oxidants and ligands and minimizes undesired homocoupling and overoxidation. Mechanistic studies have confirmed that disulfide mediates the single-electron oxidation of the alkynyl copper intermediates.
Yang et al. (Tue,) studied this question.