Redox-Mediated and Microwave-Assisted Thiol Activation: Two Approaches to Unsymmetrical Disulfides Synthesis

Two approaches to synthesis of unsymmetrical disulfides based on different types of thiol activation, namely, an electrochemical method in the presence of a redox mediator and a microwave irradiation, were discussed. The mediated electrosynthesis procedures were carried out by the oxidative coupling of thiols or by the thiol-disulfide exchange in the presence of redox pairs-substituted o-aminophenol/o-iminobenzoquinone. It has been established that the formation of unsymmetrical disulfides under electrochemical conditions occurs as a result of both the oxidative coupling of sulfur-centered radicals, and a redox-mediator promoted thiol-disulfide exchange, which led to a high yield of heterodimeric products (89%-99%). The microwave-assisted synthesis made it possible to obtain the target products with yields of 13%-86% depending on different irradiation parameters such as power, temperature, and irradiation duration. However, this method requires a rigorous selection of conditions for each reaction and is therefore inferior to the electrochemical approach.

Automated summary

Two approaches to synthesis of unsymmetrical disulfides, namely electrochemical method and microwave irradiation, were discussed. The oxidative coupling of sulfur-centered radicals and a redox-mediator promoted thiol-disulfide exchange were found to be the main mechanisms of the electrochemical method. Microwave-assisted synthesis showed variable yields depending on irradiation parameters.