Synthesis and Properties of Ethyl 1-Aryl-5-methyl4-[1-(phenylhydrazinylidene)ethyl]-1H-pyrazole-3-carboxylates

Ethyl 1-aryl-4-acetyl-5-methyl-1H-pyrazole-3-carboxylates reacted with phenylhydrazine to give the corresponding hydrazones, ethyl 1-aryl-5-methyl-4-[1-(phenylhydrazinylidene)ethyl]-1H-pyrazole-3-carboxylates, which were converted to ethyl 1'-aryl-4-formyl-5'-methyl-1-phenyl-1H,1'H-3,4'-bipyrazole-3'-carboxylates by treatment with the Vilsmeier-Haack reagent. No indole derivatives were formed from the same hydrazones under the Fischer reaction conditions, but cyclization to 2-aryl-3,4-dimethyl-6-phenyl-2,6-dihydro-7H- pyrazolo[3,4-d] pyridazin-7-ones was observed.