The electrochemical reductive cleavage of a p-nitro-1,3-dioxolane and a p-nitro-1,3-dioxane in basic aqueous ethanol at Hg: electrolabile protecting groups of ketones

The electroreductive cleavage of 4-(4′-nitrophenyl)-1,3-dioxolane (1) and of 7-nitro-1,3-benzodioxane (7) was studied at Hg in a basic hydroethanolic medium (EtOH+H2O 60:40 v/v, 0.15 M KOH). The voltammograms show classical behavior: peaks for the reversible substrate/radical anion redox couples (1/1− and 7/7−), a peak corresponding to further reduction of the radical anion to the hydroxylamine and peaks for the hydroxylamine/nitroso reversible redox couple at less negative potentials. Preparative electrolyses performed at the potential of the formation of the radical anion gave, in very good yields, cyclohexanone resulting from cleavage of the radical anion and show that these ketals are good electrolabile protecting groups. The influence of the electrolysis temperature is discussed. The electroreductive cleavage in basic ethanolic medium is more efficient than in aprotic medium.