Electron-transfer processes: metal salt catalysed oxidation of olefins by peroxydisulphate

Abstract

The reaction of simple olefins (oct-1-ene, oct-2-ene, cyclohexene, cycloheptene) with peroxydisulphate has been investigated under several conditions: (i) in aqueous medium and catalysis by Ag^I, Fe^II, and Cu^II; (ii) in acetic medium and catalysis by Cu^II, Fe^III; (iii) in the presence of traps of nucleophilic alkyl radicals (protonated heteroaromatic bases and 1,4-benzoquinone either in water or in acetic acid). The catalyst and the radical trap govern the selectivity and allow a variety of new synthetic achievements. Evidence for a unified initial mechanism of electron transfer with formation of a radical cation from the olefin is reported to explain all the results. In water the radical cation gives a β-hydroxyalkyl radical, which, depending on the nature of the catalyst and the trap, can give the corresponding saturated alcohol by hydrogen abstraction, the products of Cu^II oxidation, or β-hydroxyalkylation of the heteroaromatic compound or 1,4-benzoquinone. In acetic acid the radical cation gives a β-acetoxyalkyl radical, which is oxidized to the corresponding allylic acetate by copper(II) acetate or trapped by the heteroaromatic base.