Facile access to some new 3,3′‐bipyrazole‐ester derivatives utilizing bis‐hydrazonoyl chlorides

The 1,3‐dipolar cycloaddition reaction of bis‐hydrazonoyl chlorides with ethyl propiolate and dimethyl acetylenedicarboxylate afforded diethyl 1,1′‐aryl‐3,3′‐bipyrazole‐4,4′‐dicarboxylate and tetramethyl 1,1′‐diaryl‐3,3′‐bipyrazole‐4,4′,5,5′‐tetracarboxylate esters, respectively. Heating the latter two compounds with a mixture of HCl/AcOH furnished the same product: 3,3′‐bipyrazole‐5,5′‐dicarboxylic acid. Reaction of the tetracarboxylate ester with aniline derivatives and with hydrazine gave the corresponding bipyrazole‐fused heterocycles. Heating the dicarboxylic acid with 2‐aminothiazole gave the corresponding bis‐amide derivative. The structures of the products were established by elemental analysis, spectral data, and single‐crystal X‐ray crystallography.