A comparative study of the oxidation of oct-1-ene by mercury(II), thallium(III), and lead(IV) acetates in methanol

Abstract

A comparative study has been made of the oxidation by mercury(II), thallium(III), and lead(IV) acetates of a monosubstituted aliphatic olefin (oct-1-ene) in methanol. Reaction proceeds in two stages. In the first step, electrophilic addition occurs to give an organometallic adduct in which a methoxy-group is incorporated at C-2. There is no evidence for concerted addition of the two substituents. The adduct from mercury(II) is essentially stable under the reaction conditions but those from thallium(III) and lead(IV) decompose in three competing ways: (i) an acetate group is transferred from the metal atom to C-1 in an S_Ni process; (ii) a carbonium ion is generated on heterolysis of the carbon–metal bond and this undergoes competitive hydride shift and nucleophilic attack; (iii) anchimeric assistance to heterolysis is provided by the neighbouring methoxy-substituent which preferentially migrates to C-1 on collapse of the resultant ion-pair. The relative importance of these three processes is governed by the leaving-group capacity of the metal substituent and by the nature of the ligands on the metal.