EPR spectroscopy and polarography of nitroazoles. 3. Nitropyrazoles

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

“…O Extensive series of nitroazoles were investigated systematically by ESR and polarography (T. I. Vakul'skaya, V. A. Lopyrev, et al), and the mechanisms of their electrochemical reduction and the structure and properties of the intermediate radical-ions were studied [292][293][294][295][296][297][298]. In contrast to NH-nitroazoles the transfer of the first electron is reversible for N-alkylnitroazoles, and at the first stage of reduction they form stable primary radical-anions that undergo further reduction to hydroxyamino derivatives.…”

Radical-anions in the vicarious C-amination reactions of N-substituted nitrotriazoles

“…2). We obtained the radical-anion i with similar constants earlier by the electrochemical reduction of 1-methyl-3-nitro-1,2,4-triazole in an aprotic medium [16,18].…”

“…Apparently, overlap of the orbitals of the unshared electron pairs of adjacent pyridine nitrogen atoms or increase in the aromaticity of the system help to reduce the energy of the LUMO and facilitate the transfer of an electron to the molecule being reduced. However, in spite of the fact that nitroazoles unsubstituted at the nitrogen atom are reduced at the first stage more readily than their N-alkylated derivatives [15][16][17][18][19][20][21][22], mononitro-substituted pyrazoles, imidazoles, and benzimidazoles with unsubstituted nitrogen atoms are not aminated under the conditions of the vicarious nucleophilic substitution of hydrogen [9,10,[23][24][25]. This can be explained by the fact that not only the reagent but also the substrate (the mononitroazole) unsubstituted at the nitrogen atom undergoes deprotonation in a highly basic medium, and as a result electron transfer from the anion of the reagent to the anion of the substrate becomes unlikely if not impossible.…”