The oxidation of benzylic groups to the corresponding carboxylic acid functionality by dioxygen is mediated by a combination of nitrogen oxides and selenium dioxide (SeO2). Substrates examined include alkylnaphthalenes and alkylpyridines. The aldehyde appears to be an intermediate in the reaction. Mechanistic studies suggest that the rate-determining step is hydrogen atom abstraction by nitrogen dioxide (NO2) to form the benzyl radical. Selenium dioxide subsequently oxidizes this radical to the desired product. (C) 2003 Elsevier Science B.V. All rights reserved.