Synthesis and thermal reaction of 2,2-diacyl-N-(1-pyridinio)vinylaminides: formation of pyrazolo[1,5-a]pyridines and isoxazoles

Abstract

2,2-Diacyl-N-(1-pyridinio)vinylaminides have been prepared by the reaction of pyridine N-imides with 1,1-diacyl-2-ethoxyethylenes. Refluxing the bisethoxycarbonylvinylaminides (VIa, b, and d–f) in xylene afforded the ethyl pyrazolo[1,5-a]pyridine-3-carboxylates (Xa, b, and d–f); however the diacetylvinylaminides (IVa–c) and the acetyl(ethoxycarbonyl)vinylaminides (Va–c) are thermally labile and, upon heating in benzene, undergo N–N bond cleavage to give isoxazole derivatives [(XV) and (XVI)] in high yields.