Selective Syntheses of Unsymmetrical Diaryl Sulfides Enabled by a Sulfur Dioxide Surrogate as a Divalent Sulfur Source and an Activating Agent

Organic sulfides are prevalent in nature and artificially synthesized molecules, including pharmaceuticals, agrochemicals, and functional materials. However, existing methods of synthesizing organic sulfides have limitations, such as the use of unstable, prefunctionalized sulfur sources and the need for additional synthetic steps. While effective for symmetrical and cyclic sulfides, few methods have been reported for synthesizing simple unsymmetrical sulfides via single three-component reactions. Therefore, in this study, a highly selective general method of synthesizing unsymmetrical diaryl sulfides, enabled by a Cu catalyst and potassium metabisulfite (K2S2O5), which is a sulfur dioxide (SO2) surrogate, is established. The three-component synthetic method offers safe, convenient access to unsymmetrical sulfides without using hazardous SO2 gas and preformed C–S bond-containing compounds such as thiols and disulfides. The detailed reaction mechanism supported by theoretical calculations is analyzed, indicating the roles of SO2 as a divalent S source as well as an activating agent for deoxygenation at the S atom.