Metal-free C–S coupling of thiols and disulfides

In organic synthesis, transition-metal and photoredox-catalysis-based reaction systems are emerging trends for the construction of C-S bonds. Many review articles have recently appeared in this field; however, we present herein an overview of metal-free C-S coupling reactions using thiols or disulfides as sulfur surrogates. The oxidants we have considered include peroxides, tert-butyl nitrite (TBN), DDQ, iodine reagents, and molecular oxygen. In addition, selective electrochemical oxidative transformations are also covered with mechanistic details.