Réduction électrochimique de γ-nitrocétones. Conditions expérimentales d'accès à des dérivés de la pyrroline et de la pyrrolidine

Abstract

Optimal conditions for electrosynthesis, at a mercury cathode in hydroalcoholic media, of three classes of nitrogen heterocyclic compounds are set up from an exhaustive study of the electrochemical behaviour of γ-nitroketones 1 and their reduction products.Pyrroline-N-oxides 3 are obtained by cyclization of the hydroxylamine when the nitro compounds are reduced at sufficiently low cathodic potentials. Quantitative yields are achieved in the case of tertiary nitro compounds. In other cases (primary and secondary nitro compounds), simultaneous formation of ketone-oximes 6 occurs.According to the nature of the α-substituent of the carbonyl, the other heterocyclic derivatives can be prepared as follows. In the case of a methyl substituent, pyrrolines 4 can be obtained by reduction of nitro compounds 1 or of N-oxyde pyrrolines 3. Pyrrolidines 5 are prepared by reduction of 1, or 3 and 4 in the case of tertiary compounds. In the case of a phenyl substituent, pyrrolines 4 can only be obtained by reduction of compounds 3 arising from a tertiary nitro compound. Pyrrolines 5 are prepared by direct reduction of 1 (primary and secondary nitro compounds) or of 3 and 4 (tertiary nitro compounds).