Electro-organic reactions. Part 24. Preparative and mechanistic aspects of the anodic oxidation of dithioacetals and 1,3-dithianes

Abstract

Anodic oxidation of the title compounds is a convenient and efficient method for deprotection, i.e. for the regeneration of carbonyl compounds.

A detailed investigation of the sulphur-containing products confirmed that the initial, 2 F mol^–1, products are disulphides which, in aqueous acetonitrile, are oxidised further to alkyl alkanethiosulphinates and the corresponding thiosulphonates. In some cases alkyl polysulphides and N-alkylacetamides are important products. Unsymmetrical dithioacetals are oxidised anodically to the three possible disulphides, i.e. cross-coupling occurs. Unsymmetrical disulphides are similarly oxidised to a complex mixture of symmetrical and Unsymmetrical thiosulphinates and thiosulphonates.

These results, combined with those of cyclic voltammetric and coulometric experiments, suggest a mechanism in which the key step is carbon–sulphur bond cleavage in the initially formed radical cation. The direction of the cleavage is determined by understandable substituent effects.