Catalytic oxidation of C-C bond is a key technology to transform petroleum -based as well as sustainable biomass feedstock into more valuable oxygenates. We herein describe a convenient and useful oxidation strategy of converting ketones into carboxylic acids using homogeneous copper catalyst without additives and with O-2 as the terminal oxidant. A wide range of aryl and aliphatic ketones as well as beta-O-4 lignin models were selectively oxidized to acids via C C bond cleavage. Mechanism studies by EPR and in situ NMR elucidate the principles of Cu/O-2 reactivity that involves C-H bond and O-2 activation via a peroxide species. This provides an important foundation for expanding the scope of useful aerobic oxidation reactions using copper catalysts. (C) 2016 Elsevier Inc. All rights reserved.