A new method was demonstrated to overcome the selectivity issue of radical-radical cross-coupling toward the synthesis of asymmetric diaryl thioethers. The preliminary mechanism was revealed by radical-trapping experiments, DFT calculations, and kinetics, etc., indicating that the C-S bond formed through cross-coupling of a thiyl radical and an aryl radical cation. Moreover, the formation of an aryl radical cation instead of the C-H bond cleavage was determined as the rate-limiting step.

By utilizing elemental sulfur as the thiolation agent and oxidant, a copper-catalyzed direct C-H bond thiolation of electron-deficient arenes was demonstrated. Various electron-deficient arenes were proved to be suitable for this transformation. Preliminary mechanistic studies indicated that this reaction underwent a radical pathway, in which the trisulfur radical anion (S˙) might play a vital role. Meanwhile, KIE experiments suggested that C-H bond cleavage was not involved in the rate-determining step.

Selective C-H bond activation and functionalization is an invaluable and eco-friendly tool for new chemical bond construction. Recently, great progress has been made in the highly selective ortho- and meta-C-H bond functionalization of arene derivatives. In contrast, the remote para-C-H bond functionalization still remains a challenge. Herein, an oxidation-induced strategy for para-selective C-H bond functionalization of iodobenzenes towards the synthesis of various useful asymmetric diaryl ethers was demonstrated. This strategy not only provides a novel method for para-C-H bond functionalization, but also proposes a general idea for the development of new, highly selective para-C-H functionalization reactions.

The preliminary mechanism of this reaction is revealed by radical‐trapping experiments, DFT calculations and kinetics, indicating that the C—S bond is formed through cross‐coupling of a thiyl radical and an aryl radical cation.