Synthesis of 1,4-Benzothiazines via KI/DMSO/O2-Mediated Three-Component Oxidative Cyclization/Coupling

A three-component transition-metal-free aerobic method for the generation of 1,4-benzothiazines is reported herein. The KI/DMSO/O-2 system was found to be effective for the oxidative cyclization/coupling of 2-aminobenzenethiols, anilines, and methylketones. Hence, various structurally important imino 1,4-benzothiazines were assembled with broad functional group tolerance. Mechanistic studies revealed an initial oxidation of ketone alpha C-H bonds by the KI/DMSO/O-2 oxidative system.