Heterocyclic synthesis with ω-bromoacetophenone: Synthesis of some new pyrazole, pyridazine and furan derivatives

Abstract

p-Bromophenacylnitrile derivatives 3a,b react with hydrazine
derivatives under different conditions to afford the
diaminopyrazoles 4a,b, the pyridazine-6-imines 5a,b,
and 5-aminopyrazoles 11a,b. Refluxing of 5a in ethanol/
hydrochloric acid mixture furnished its transformation into the pyridazine-6-one 6 while 5b under the same reaction conditions, underwent ring contraction expelling phenyl hydrazine to afford the furan derivative 7.
Compound 7 could also be obtained from 3a upon reflux
in ethanol catalyzed by triethylamine. Ethyl  phenacylcyanoacetate 3b reacts with hydrazine hydrate and phenylhydrazine to afford the 4-phenacylpyrazole derivatives
11a,b respectively. Compound 3b afforded a mixture of
the two furan derivatives 12 and 13 upon reflux in ethanol
catalyzed by triethylamine. Compound 3b also undergoes
the coupling reaction with the aromatic diazonium
salts 14a-d to afford the pyrazole derivatives 16a-d presumably
via the hydrazo derivatives 15a-d respectively.