Decatungstate-Catalyzed Photooxygenation of S-2-Phenylbutane and Cumene via a Free Carbon-Radical Intermediate

The decatungstate W10O32 4- catalyzed photooxygenation of cumenes in the presence of molecular oxygen and triethylsilane has been thoroughly studied. In all cases the corresponding tertiary hydroperoxides were formed as the major products. Based on stereoisotopic studies as well as on primary and β-secondary isotope effects, we provide strong evidence for a stepwise mechanism, in which a hydrogen atom abstraction occurs in the rate-determining step of the reaction. In addition, the oxidation of (S)-2-phenylbutane by decatungstate/Et3SiH catalytic system, shows the formation of the two enantiomeric alcohols, (R)-2-phenylbutan-2-ol and (S)-2-phenylbutan-2-ol, in equimolar amounts. This product racemization confirms further the presence of a stepwise mechanism and support the formation of a free carbon-centered radical intermediate.