Intramolecular reactions. Part VIII. Interception of sulphenate esters formed in the rearrangement of sulphoxides

Abstract

Allyl p-tolyl sulphoxide reacts with methanolic sodium methoxide by initial prototropic isomerisation and subsequent addition of methanol to give 2-methoxypropyl p-tolyl sulphoxide. By contrast, reaction with piperidine yields, as the principal products, allyl alcohol and N-p-tolylsulphenylpiperidine. These are formed by nucleophilic displacement at sulphur in the isomer, allyl toluene-p-sulphenate which is in equilibrium with the sulphoxide.

Propenyl p-tolyl sulphoxide also gives the sulphenamide under similar conditions and the marked effect of solvent upon the product distributions in these reactions is explained in terms of the competition between prototropy, nucleophilic addition, and nucleophilic attack on the sulphenate.

α-Naphthylmethyl p-tolyl sulphoxide yields the same sulphenamide in reactions with piperidine; diversion of a sulphenate ester is again implicated and the results support postulates made by others about the mechanisms of sulphoxide racemisation.