Reactions of lead tetra-acetate. Part XIX. Oxidation of the dimethoxybenzenes: the behaviour of lead tetra-acetate as an ambident electrophile

Abstract

The capacity of lead tetra-acetate to act as an ambident electrophile has been examined by studying its reactions with the three dimethoxybenzenes. For one of the types of reaction, plumbylation, evidence is adduced that the meta-isomer is the most reactive, as expected for an electrophilic substitution by the S_E2 mechanism. In contrast, this isomer is the least reactive in the second type of reaction, acetoxylation, and possible mechanisms to account for the characteristics of this reaction which involve the removal of either one or two electrons from the aromatic ring are discussed. Electrophilic plumbylation is a readily reversible process, but, at least for p-anisyl-lead triacetate, a homolytic pathway in which the lead group is replaced by hydrogen also occurs.