Cathodically promoted addition of nitromembrane to aldehydes and exploratory studies of the mechanism of the electrochemical reduction of the nitroolefins so produced

Addition of nitromethane to aromatic and heteroaromatic aldehydes has been carried out in nitromethane. The reaction is catalyzed by superoxide produced by cathodic reduction of dioxygen, which serves as an electrogenerated base. The initially formed products are nitroalcohols which undergo dehydration, either in situ or in a subsequent chemical dehydration, to give 1-nitroalkenes. The addition of nitroethane to benzaldehyde, thiophene-2-carboxaldehyde, and furan-2-carboxaldehyde was also investigated, and good yields of diastereomeric mixtures of the nitroalcohols were obtained. The electrochemical reduction of seven of the 1-nitroalkenes prepared in this and earlier work was studied by cyclic voltammetry and controlled potential coulometry. The reduction is thought to proceed by initial formation of the radical anion which subsequently dimerizes. However, in many cases, the reduction is accompanied by oligomerization of the starting material, leading to coulometric n-values that are much less than one.