Mechanistic insights on base-DMSO mediated aerobic oxidation of (hetero)benzylic C-H bonds

Abstract

Aerobic oxidation of (hetero)benzylic C-H bonds to ketone products always relies on radical process initiated by transition-metal catalysis. Using inorganic bases, here we report an efficient transition-metal-free strategy, which is enabled by DMSO as both the high-polar solvent and the effective reductant. The ionic mechanism was suggested for this reaction, and a high yield of ketones was obtained by choosing the alkalinity-matched inorganic base with the acidity of (hetero)benzylic C-H bonds. Via kinetic experiments, a mixed mechanism with two reaction pathways was suggested for the generation of ketones, one of which involved the reduction of peroxide intermediates toward alcohols intermediates by DMSO, while the dehydration of peroxide intermediates lead to the direct formation of ketones in the other pathway. These findings not only provide a greener approach for ketones production from (hetero)benzylic oxidation, but also encourage the possible strategy to generate alcohols under inorganic base catalysis.