Free radicals in vicariousC-amination reactions of 1-methyl-4-nitropyrazole

Abstract

The primary radical anions of substrate in the reactions of vicarious nucleophilic substitution of hydrogen in 1-methyl-4-nitropyrazole with 1,1,1-trimethylhydrazinium iodide and 4-amino-1,2,4-triazole in t-BuOK-DMSO were observed and identified by EPR monitoring. The probable mechanism of the substrate radical anions formation is discussed.

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)

“…The vicarious nucleophilic substitution of hydrogen was first used by V. A. Lopyrev, G. V. Dolgushin, and coworkers for the C-amination of N-methylnitroazoles by 1,1,1-trimethylhydrazinium halides 114 or 4H-1,2,4-triazole-4-amine 115 in superbasic media [299][300][301][302][303][304][305][306]. …”

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

“…We found the answer to this question by comparing the results from investigation of the vicarious C-amination of the nitro derivatives of 1,2,3-and 1,2,4-triazoles by ESR and the analogous results that we obtained earlier for 1-methyl-4-nitropyrazole [12], 1-methyl-4-nitroimidazole [9,10], and 1-methyl-5-and 1-methyl-6-nitrobenzimidazoles [11] with the data from quantum-chemical calculations of the spin density distribution in the radical-anions of the substrates a-i. It was found that the The calculated spin density at the CH carbon atoms in the radical-ions of nitroazoles amination of all the above-mentioned compounds takes place exclusively at carbon atoms with sufficiently high positive spin density in their radical-anions.…”

“…As expected, ESR monitoring showed that the reaction mixture of the N-unsubstituted nitrotriazole 6 with the iodide 2 was diamagnetic, and this agrees with the absence both of the blue-violet color in the reaction mixture and of the amination product. It was unexpectedly found that 1-methyltriazole 7, unlike other N-protected nitroazoles [10][11][12], also does not form amination products under the conditions of the vicarious nucleophilic substitution of hydrogen, although in this case the reaction mixture was colored, and a signal for the primary radical-anion of 1-methyl-3-nitro-1,2,4-triazole (g = 2.0032) appeared in the ESR spectrum with signals and HFS constants, mT: triplet (N-NO 2 , 1.178); doublet (1H, 0.440); triplet (1N, 0.160); triplet (1N, 0.120); triplet (1N, 0.050); quartet (3H-CH 3 , 0.050) (Fig. 2).…”

“…In a continuation of our investigations into the vicarious C-amination of nitroazoles containing two nitrogen atoms in the five-membered ring [9,10,12] and the condensed analogs of imidazole (nitrobenzimidazoles) [11] in the present work we present the results from the amination of nitroazoles containing three nitrogen atoms in the five-membered ring, i.e., 3-nitro-1,2,4-triazoles and 4-nitro-2-phenyl-1,2,3-triazole.…”

“…Having put forward the idea of possible electron transfer during the vicarious nucleophilic substitution of hydrogen [9] and having confirmed this for the vicarious amination of nitrobenzene and a series of N-methylated nitroazoles [10][11][12], we assumed that the lower the reduction potential of the nitroazole the more readily the latter should undergo amination in the vicarious nucleophilic substitution of hydrogen. Our papers on the electrochemical reduction of azoles in an aprotic medium [13,14] show that their first reduction potentials decrease both with the accumulation of nitrogen atoms in the heterocycle and with the introduction of phenylene fragments.…”