Utility of cyano acid hydrazide in heterocyclic chemistry: A new route for the synthesis of new 1,2,4-triazolo[1,5-a]pyridines and 1,2,4-triazolo[1,5-a]isoquinolines

Cyano acid hydrazide 1 was condensed with cyclohexanone in refluxing ethanolic piperidine to yield the hydrazone 4. Compound 4 reacts with arylidines 5a-i to yield the 1,2,4-triazolo[1,5-a]pyridines 7a-i. Compound 4 also reacts with mixtures of aliphatic aldehydes and different active methylene reagents to yield 1,2,4-triazolo[1,5-a]pyridines 8a-d. Similarly reaction of 4 with arylazomalononitrile to yield the triazolopyridines 10a-d. Reaction of 4 with aromatic aldehydes gives 12a-e. Compound 8a reacts with elemental sulfur to yield the thieno-1,2,4-triazolopylidine 13. This underwent cycloaddition with acrylonitrile, omega-nitrostyrene, chalcone, N-phenylmalemide, dimethylacetylenedicarboxylate and tetracyanoethylene yielding the isoquinolines 15-18. All new compounds have been characterized by their IR, H-1 NMR and mass spectra.