A new liquid-phase catalytic oxidation system for the low temperature, high conversion benzylic mono-oxyfunctionalization of 10,11-dihydrocarbamazepine (1) into oxcarbazepine (4) with dioxygen has been developed. The method is based on a co-oxidation of 1 with benzaldehyde in the presence of a four-component catalyst system consisting of Co(-OAc) 2 , Ni(OAc) 2 , Cr(NO 3 ) 3 , and N-hydroxyphthalimide (NHPI). The influence of the catalyst system on the formation and decomposition of the crucial hydroperoxide intermediate