Cyclisation reactions of azolylhydrazones derived from ethyl cyanoacetate and malononitrile. Formation of azolo[5,1-c][1,2,4]triazines

Abstract

Ethyl 2-cyano-2-(1,2,4-trizol-5-ylhydrazono)acetate (2a) cyclised in aqueous ethanol to a mixture of ethyl 7-amino-1,2,4-triazolo[5,1-c][1,2,4]triazine-6-carboxylate (3a) and 4,7-dihydro-7-oxo-1,2,4-triazolo[5,1-c]-[1,2,4]triazine-6-carbonitrile (4a); in acetic acid the product was mainly the amino-ester (3a) whereas in pyridine or collidine, salts of the oxo-nitrile (4a) were formed exclusively. Similar solvent effects controlled the cyclisation of the cyano(pyrazol-5-ylhydrazono)acetate (2c), but the corresponding cyano(tetrazol-5-ylhvdrazono)acetate (2d) gave only the amino-ester (3d) in acetic acid or pyridine. 2-(1,2,4-Triazol-5-ylhydrazono)malononitrile (17) cyclised unambiguouly to 7-amino-1,2,4-trizolo[5,1-c][1,2,4]triazine-6-carbonitrile (18) in acetic acid or aqueous ethanol.

Drastic hydrolysis of the hydrazones (2a) and (17) and the triazolo[5,1-c][1,2,4]triazines (3a), (4a), and (18) with 6N-hydrochloric acid gave a hydrate of 1,2,4-triazolo[5,1-c][1,2,4]triazin-7(4H)-one (24). Selective hydrolysis of the same triazolotriazines afforded intermediates which were identical with known derivatives and which served to establish the [5,1-c] geometry of ring fusion. Mass spectral fragmentation of 7-aminoazolo[5,1-c]-[1,2,4]triazines confirms that the azole ring is more stable than the 1,2,4-triazine ring on electron impact.