Synthesis of 1H-pyrazolo[3,2-c]-s-triazoles and derived azamethine dyes
The condensation of ethyl 5-hydrazino-3-methylpyrazole-4-carboxylate with various aldehydes and acid chlorides is outlined. The cyclisation of the resulting hydrazones and hydrazides, under oxidative and dehydrative conditions, respectively, gives ethyl 1H-pyrazolo[3,2-c]-s-triazole-7-carboxylates. Hydrolysis of these esters followed by decarboxylation of the corresponding acids, gives 1H-pyrazolo[3,2-c]-s-triazoles. Another method of synthesis of 1H-pyrazolo[3,2-c]-s-triazoles, involves the condensation of S-methylisothiocarbohydrazide hydroiodide with β-oxo-esters. The synthesis of a range of azamethine dyes containing the pyrazolo[3,2-c]-s-triazole nucleus is described, and the absorption properties of these dyes are discussed.