Cobalt-catalyzed synergistic oxidation of benzylic C-H bonds using ozone and hydrogen peroxide.

Oxidative transformation of benzylic C(sp3)-H bonds into carbonyl functionalities under mild conditions offers an efficient and versatile strategy for synthesizing high-value aromatic carboxylic acids and ketones. Herein, we report a cobalt-catalyzed method for the oxidation of benzylic C(sp3)-H bonds to access carboxylic acids and ketones under mild conditions via continuous O3 bubbling. Ozone and hydrogen peroxide serve as sustainable and environmentally benign co-oxidants, while benzyltriethylammonium bromide (TEBA) acts as an efficient phase-transfer catalyst. This protocol exhibits high yields, excellent chemoselectivity, a broad substrate scope, and operational simplicity. The reaction mechanism has been systematically investigated through control experiments and spectroscopic studies, and the demonstrated practicality, scalability, and efficiency highlight the potential of this method for widespread application in the oxidation of inert C-H bonds.