One Electron Oxidation of a-Alkylbenzyl Alcohols Induced by Potassium 12-Tungstocobalt(III)ate. Comparison with the Oxidation Promoted by Microsomal Cytochrome P450

The chemical and microsomal oxidations of a number of 4-methoxy substituted alpha-alkylbenzyl alcohols 4-MeOPhCH(R)OH (E-ox = 1.6-1.7 V vs SCE) were investigated. Using potassium 12-tungstocobalt(III) ate, a bona fide one electron oxidant, competition between C-alpha-H and C-alpha-C-beta bond cleavage in the intermediate radical cation was observed when the side-chain alkyl group R was Et (2) and iPr (3). With R = Me (1), only C-H bond cleavage took place, whereas with R = tBu (4) C-C bond cleavage was the exclusive fragmentation process. In contrast, the microsomal oxidation of the two substrates 3 and 4 led in both cases to the exclusive formation of the corresponding ketone. Thus, an electron transfer mechanism appears unlikely for the microsomal oxidation of alpha-alkylbenzyl alcohols, even though the oxidation potential of these species is lower than or comparable to that of the active oxidant in the enzyme. A hydrogen atom transfer mechanism is more in line with these results.