Metal-Free Photocatalytic Aerobic Oxidation of Thiols to Disulfides in Batch and Continuous-Flow

Disulfides represent significant molecular and structural features in various biologically active compounds and fine chemicals. Therefore, the development of mild, efficient and sustainable methods to access disulfides is of great importance. Here, we describe the development of a mild metal-free photocatalytic aerobic oxidation of thiols to disulfides using Eosin Y and visible-light irradiation. A continuous flow procedure was developed to accelerate the photocatalytic process, enabling the preparation of disulfides with high purity in a time-frame of minutes. The mildness and applicability of our method was exemplified by the flow synthesis of the cyclic peptide hormone, oxytocin, requiring only a 200 s reaction time and an efficient one-pot batch protocol for the preparation of the therapeutic thiuram disulfide, disulfiram.