Synthesis of new pyridines and 1,2,4-triazolo [4,3-a] pyridines

ABSTRACT

Reaction of 3-cyano-4,6-disubstituted-2-oxo-1,2-dihydropyridine 1a with phosphorus pentasulfide gave the corresponding 2-thio-1,2-dihydropyridine 3. The reaction of compounds 1a,b with mixture of phosphorus oxychloride and phosphorus pentachloride afforded the 2-chloropyridine derivatives 4a,b. Treatment of 4a,b with hydrazine hydrate gave the corresponding 2-hydrazino derivatives 5a,b. Reaction of 5a,b with acid chlorides and carbon disulfide afforded the corresponding 1,2,4-triazolo [4,3-a] pyridines 7a,g and 8a,b, under the conditions of reacting compound 5a,b with the above-mentioned reagents, the cyano group was completely hydrolyzed to carboxylic acid. On the other hand, conversion of 5a,b into Schiff bases 6a,h followed by cyclization with bromine in acetic acid produced compounds 7a,g