Photocatalytic generation of alkoxysulfonium ions for selective oxidation of benzylic/allylic halides to carbonyls under base-free conditions

Abstract

Selective oxidation of organic molecules to carbonyls is a highly desirable but still challenging transformation in both synthetic chemistry and the pharmaceutical industry. Herein, we report a visible-light photocatalytic oxidation of benzylic/allylic halides to carbonyl compounds enabled by a consecutive photoinduced electron transfer (ConPET) and HAT catalysis under base-free conditions. By synergistic combination of an organophotocatalyst 4CzIPN and a thiol HAT reagent in dimethyl sulfoxide (DMSO), a broad range of halides including benzylic, allylic, and even aliphatic halides were smoothly converted into their corresponding aldehydes/ketones in moderate to excellent yields with good functional group tolerance. The robustness of this protocol is further strengthened by selective oxidation of polyhalo compounds and hybrid halo-hydroxyl compounds and controllable oxidation of bioactive molecules. Mechanistic investigation unveils a photocatalytic generation of alkoxylsulfonium ion with DMSO followed by a photoredox assisted decomposition of this species into carbonyl.