Synthesis of New Pyrazolo[1,5-α]quinazoline Derivatives

The reaction of various anthranilic acid derivatives or their esters with 4-oxotetrahydrothiophene-3-carbonitrile 2, 2-oxocyclopentanecarbonitrile (9, n = 1) or 2-oxocyclohexanecarbonitrile (9, n = 2) in ethanol under reflux conditions giving rise the formation of single products isolated in each case after simple filtration. The products were characterized as pyrazolo[1,5-a]quinazolin-5-ones 4 instead of the expected pyrazol-3-amines 3. These cascade condensation–intramolecular acylation processes generated in one-step reactions from simple starting materials novel heterocyclic scaffolds ready for further functionalization. The present synthetic protocol provides acceptable yields of new tetracyclic products in high purity.