MECHANISM OF PALLADIUM-CATALYZED ALLYLIC ACETOXYLATION OF CYCLOHEXENE

The mechanism of the quinone-based palladium-catalyzed oxidation of cy clohexene to allylic acetate was studied under various reaction condit ions with 1,2-dideuterocyclohexene (62-74% D) as the substrate. The re actions gave a 1:1 mixture of 1,2-dideutero- and 2,3-dideutero-1-aceto xy-2-cyclohexene (2 and 3, respectively), as determined by H-1 NMR spe ctroscopy. Control experiments with 1-deutero-1-acetoxy-2-cyclohexene showed that no 1,3-allylic transposition of the acetoxy group occurred under the reaction conditions employed for the allylic acetoxylation. These results provide evidence for a (pi-allyl)palladium intermediate in the quinone-based palladium-catalyzed allylic acetoxylation. With added chloride ligands and extended reaction times, bis-allylic acetat es were formed. The presence of a stoichiometric amount of CH3SO3H led to the formation of a homoallylic acetate.