Synthesis of 5-Substituted N -Nitro-2,4-dihydro-3 H -1,2,4-triazol-3-imines
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he 80th anniversary of V.M. Berestovitskaya
Synthesis of 5-Substituted N-Nitro-2,4-dihydro-3H-1,2,4-triazol-3-imines O. Yu. Ozerovaa,*, T. P. Efimovaa, and T. A. Novikovaa a
Herzen State Pedagogical University of Russia, St. Petersburg, 19186 Russia *e-mail: [email protected] Received May 6, 2020; revised May 6, 2020; accepted May 16, 2020
Abstract—The reaction of N-amino-N″-nitroguanidine with carboxylic acid chlorides at room temperature gave the corresponding N-(N″-nitroguanidino)carboxamides which underwent cyclization on heating in aqueous alkali to afford N-nitro-1,2,4-triazol-3-imines. The latter were also synthesized in a one-pot fashion. The products were characterized by 1H and 13C–{1H}, IR, and UV spectra. Keywords: N-amino-N″-nitroguanidin, carboxylic acid chlorides, N-(N″-nitroguanidino) carboxamides, N-nitro1,2,4-triazol-3-imines
DOI: 10.1134/S1070363220080046 Search for readily available polyfunctional substrates for directed synthesis of various linear and heterocyclic structures is an important problem. Organic guanidine derivaties are promising as such substrates. In most cases, they act as highly reactive nucleophiles. N-AminoN″-nitroguanidine has been shown to behave as a reactive nucleophile toward carbonyl compounds [1–4], carboxylic acids and their derivatives [5–8], functionalized nitroalkenes [9–12], and dicarbonyl compounds [13–17]. In continuation of our studies on the nucleophilic reactivity of N-amino-N″-nitroguanidine (1), herein we report its reactions with carboxylic acid chlorides (Scheme 1). Compound 1 readily reacted with acetyl, benzoyl, and 4-methoxybenzoyl chlorides in anhydrous pyridine or 2-methylpyridine at room temperature to give the corresponding N-(2-nitroguanidino)carboxamides 2–4 which were isolated in up to 69% yield. Subsequent heating of amides 2–4 in aqueous alkali resulted in their intramolecular heterocyclization involving the amino and carbonyl groups to afford 5-substituted N-nitro-2,4dihydro-3H-1,2,4-triazol-3-imines 5–7. The use of 2-methylpyridine instead of pyridine was more appropriate. In this case, the procedure of isolation of condensation products 2–4 was simpler since there was no necessity of partial removal of the solvent due to
lower solubility of compounds 2–4 in 2-methylpyridine than in pyridine. N-Nitro-1,2,4-triazolimines 5, 6, and 8 were also successfully synthesized by a one-pot procedure without isolation of intermediate amides. The structure of 2–4 was confirmed by 1H and 13C–{1H} NMR, IR, and UV spectra; furthermore, the spectral characteristics and melting point of 2 coincided with those reported in [18]. The 1H NMR spectra of 2–4 showed downfield broadened signals of magnetically nonequivalent protons of the primary (δ 8.19–8.40, 8.59– 8.64 ppm) and secondary amino groups (δ 9.57–10.49, 9.79–10.38 ppm) that are typical of nitroguanidines. Signals of protons in the substituent R were observed in the expected regions. Protons of the primary amino group of the nitroguanidine fragment become magnetically nonequivalent due to H-bonding of
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