Synthesis of some novel pyrazolo[1,5-<i>a</i>]quinazolines and their fused derivatives

New pyrazolo[1,5-<i>a</i>]quinazoline-3-carbonitriles <b>4a,b</b> were obtained via cyclocondensation of 5-amino-3-cyanomethyl-1<i>H</i>-pyrazole-4-carbonitrile (<b>1</b>) with enaminones of 1,3-cyclohexanedione derivatives <b>2a,b</b> in refluxing glacial acetic acid. Condensation of compounds <b>4a,b</b> with various aromatic aldehydes furnished the corresponding arylidene derivatives <b>6a–j</b>. On the other hand, condensation of <b>4a,b</b> with o-hydroxybenzaldehydes yielded the polyheterocyclic compounds <b>10a–h</b>. Coupling of compounds <b>4a,b</b> with aryldiazonium chlorides led to formation of 2-arylhydrazono derivatives <b>12a–h</b>. Also, reaction of compounds <b>4a,b</b> with phenyl isothiocyanate, followed by addition of ethyl chloroacetate and chloroacetonitrile, afforded the polyheterocyclic compounds based on pyrazolo[1,5-<i>a</i>]quinazoline core. The reaction of compounds <b>4a,b</b> with phenyl isothiocyanate and elemental sulfur gave the thiazole-2-thione derivatives <b>25a,b</b>. The reaction of enamines of compounds <b>4a,b</b> with each of hydrazine hydrate and guanidine hydrochloride afforded pyrazolo[4″,3″:5′,6′]pyrido[4′,3′:3,4]pyrazolo[1,5-<i>a</i>]quinazolin-8-ones <b>30a,b</b> and pyrimido[5″,4″:5′,6′]pyrido[4′,3′:3,4]pyrazolo[1,5-<i>a</i>]quinazolin-9(10H)-ones <b>33a,b</b>, respectively. The structures of all the newly synthesized compounds were elucidated by elemental analyses and spectral data. The plausible mechanisms have been postulated to account for their formation.