Synthesis and characterization of novel heterocyclic derivatives of substituted pyrazole-3,4-dicarboxylic acids and pyrazole-4-carboxaldehydes

Pyrazole derivatives hold a special place among heterocyclic compounds because of their multiple biological activities. Up to now, numerous pyrazole derivatives were synthesized to investigate their biological activities and so efforts in this area continues to increase. Pyrazole ring have been found frequently in the structure of pharmaceutical agents used today. In order to contribute to the pyrazole chemistry being so important a library of pyrazole derivatives were synthesized in this study with possibly having biological activity potential. In the first part of the study, a series of amide, ester, and ureide derivatives were synthesized from pyrazole-3-carboxylic acid and its hydrolysis products pyrazole-3,4-dicarboxylic acid synthesized from furan-2,3-diones and hydrazines via ring transformation and they used as starting compounds. Also a novel dinitrile derivative was synthesized from dehydration of diamide derivative obtained from the reaction of dicarboxylic acid with ammonia. Novel diketone derivative was synthesized from Friedel-Crafts reaction starting from pyrazole-3,4-dicarboxylic acid derivative. Finally, a pyrazole-4-carboxylic acid derivative was synthesized from the decarboxylation of dicarboxylic acid. In the second part of the study, a novel pyrazole-4-carboxaldehyde derivative was synthesized under the Vilsmeier-Haack reaction conditions. First Schiff base derivatives, hydrazide-hydrazones and thiosemicarbazones of our starting compound were synthesized. In the next step a novel 1,3,4-oxadiazole derivative was obtained from the cyclization of hydrazide-hydrazone derivative in Ac2O while the cyclization of the thiosemicarbazone derivative in the same conditions produced the novel 1,3,4-thiadiazole derivatives. Also, a series of thiazole heterocycle containing pyrazole derivatives were synthesized by Hantzsch cyclization of thiosemicarbazone with substituted α-bromoacetophenones. On the other hand, a series of chalcone derivatives were synthesized by Claisen-Schmidt condensation of pyrazole-carbaldehyde with substituted acetophenones. Finally novel pyrazolylpyrazoline-sulfonamide derivatives were sythesized from the cyclization of obtained chalcones with hydrazines. The synthesized compounds were characterized by following FT-IR, 1H NMR, 13C NMR and Mass spectroscopic methods.