A New Synthesis for 1,2,4-Triazolo[1,5-a]-pyridines and 1,2,4-Triazolo[1,5-a]isoquinolines

Article abstract of DOI:10.1007/BF00844690

Condensation of cyano acid hydrazide 1 with cyclopentanone in refluxing ethanolic piperidine yields hydrazone 2. With mixtures of aliphatic aldehydes and different active methylene reagents, 2 reacts to 1,2,4-triazolo[1,5-a]pyridines (8a-f). Compound 2 also reacts with arylidenes 9a-g to give triazolopyridines 10a-g. Reaction of 2 with aromatic aldehydes affords compounds 13a-c. Diazotation of 2 with aryldiazonium chloride in ethanol at 0°C leads to the azo adducts 15a-d. The thieno-1,2,4-triazolopyridine 16 is obtained by reaction of 8a with elementary sulfur. 16 undergoes cycloaddition with ω-nitrostyrene, maleic anhydride, N-arylmalemide, and acrylonitrile yielding the isoquinolines 21-24. All new compounds have been characterized by their IR, ¹H NMR, and mass spectra.