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In continuing studies on condensed zwitterionic derivatives of 1,2,3-triazole [1-2], we proposed a simple and convenient method for synthesis of 1-imidazolylpyrrolo[1,2-c][1,2,3]triazolio-5-olate. By means of azo coupling of 5-diazoimidazole 1 with proline, we obtained triazene 2 [3], isolated as two isomers relative to the N=N bond. N N N + N NH O O EtO 2 C Me Ac 2 O Ac 2 O 1 2 3 4 5The reaction of intramolecular acylation in acetic anhydride leads to formation of pyrrolo[1,2c][1,2,3]triazolio-5-olate 3. Cyclization of triazene 4, obtained from p-tolyl-N-methylglycine and imidazole 1, leads to the zwitterionic triazole 5.The 1 H NMR spectra were taken in DMSO-d6, internal standard TMS. 1-(4-Ethoxycarbonylimidazol-1-yl)-2,4,5,6-tetrahydropyrrolo[1,2-c][1,2,3]triazolio-5-olate (3).A solution of sodium nitrite (0.186 g, 2.7 mmol) in water (10 ml) was added dropwise at 0-5°C with stirring to a solution of the ethyl ester of 5-aminoimidazole-4-carboxylic acid (0.21 g, 1.1 mmol) in 0.1 N HCl (27 ml). The end of the reaction was monitored using iodine/starch paper. The yellow solution of diazo compound 1 obtained __________________________________________________________________________________________