Triazines and related products. Part 24. Synthesis of pyrazol-4-ylidenehydrazinoimidazoles by hydrazinolysis of imidazo[5,1-c][1,2,4]-triazines and 2-arylazoimidazoles by diazonium coupling reactions

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Abstract
4-(Substituted)imidazo[5,1-c][1,2,4)triazine-8-carboxamides with ester, ketone, or cyano-groups in the 3-position undergo ring-opening with hydrazine and phenylhydrazine to yield substituted (pyrazol-4-ylidenehydrazino)imidazole-4-carboxamides. In some cases ring cleavage is initiated by attack of the hydrazine at C-4 of the imidazotriazine, and in others by nucleophilic attack at the 3-substituent. Examples of the same series of hydrazones can be prepared by coupling 5-diazoimidazole-4-carboxamide with activated pyrazoles. Diazotised arylamines couple with 5-aminoimidazole-4-carboxamide at C-2 to yield a series of intensely coloured 5-amino-2-arylazoimidazole-4-carboxamides, which can be cyclised to 8-arylazo-9H-purin-6(1H)-ones with ethyl formats in sodium ethoxide, and form mono- or di-acylamino-derivatives in formic acid or acetic anhydride. In no case was it found possible to prepare 2,5-diaminoimidazole-4-carboxamide by reductive cleavage of 5-amino-2-arylazoimidazole-4-carboxamides; only arylamines or unstable hydrazo-intermediates were identified. Reduction of 5-amino-2-(2-cyanophenylazo)imidazole-4-carboxamide with sodium dithionite or with hydrogen over a 10% palladium–charcoal catalyst afforded 5-amino-2-(3-aminoindazol-2-yl)imidazole-4-carboxamide.

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