The 1H-pyrazole-3-carboxylic acid 2 or its remarkably stable acid chloride 3 can easily be converted into the corresponding ester or amide derivatives 4 or 5, respectively, from reaction with alcohols or N-nucleophiles. Pyrazolo[3,4-d]pyridazines 6a,b are obtained from cyclocondensation reactions of the pyrazoles 2 and 3, respectively, with phenylhydrazine or hydrazine hydrate, while 6c is formed in an one-pot procedure from the furan-2,3-dione 1 and hydrazine hydrate.

This study demonstrates the ease of functionalization and cyclization reactions of 1H-pyrazole-3-carboxylic acid, leading to the formation of pyrazolo[3,4-d]pyridazines and their derivatives.

Paper

Functionalization and cyclization reactions of 4-benzoyl-1,5-diphenyl- 1H-pyrazole-3-carboxylic acid†

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