Studies with polyfunctionally substituted heteroaromatics: New routes for the synthesis of polyfunctionally substituted pyridines and 1,2,4‐triazolo[1,5‐a]pyridines

Abstract

The 1‐substituted ethylidenemalononitriles 1a–c condensed with triethyl orthoformate in refluxing acetic anhydride to yield the dienes 2a–c. On the other hand, a mixture of N,N‐dimethylformamide and triethyl orthoformate condensed with 1a–d to yield the N,N‐dimethylaminopentadienonitriles 2d–g. The pentadienonitriles 2d–g were also formed from the reaction of 1a–d with dimethylformamide dimethylacetal in refluxing acetic acid. When compounds 1a–c were treated with dimethylformamide dimethylacetal in refluxing p‐xylene, a mixture of 3,4 and 2e–g was formed. The reaction of 2a,b with hydrazine hydrate afforded the N‐amino‐2‐iminopyridines 5a,b. These were converted into the triazolo[1,5‐a]pyridines 8a–d on treatment with benzoyl chloride and with dimethylformamide dimethylacetal. On the other hand, the reaction of 2c with hydrazine hydrate afforded the pyrazolo[3,4‐b]pyridine 7c. Treatment of 2a,c or 2e,g with cyanoethanoic hydrazide afforded the N‐(cyanoacetamido)pyridines 9a,b. The dienes 2d,f,g afforded the pyridones 11a–c on treatment with acetic acid and hydrochloric acid mixture. Compounds 11b,c were also formed on treatment of 2b,c with acetic acid hydrochloric acid mixture. The reaction of 2d,g with ethanolic sodium ethoxide gave the ethoxypyridines 13a,b.