Studies on heterocyclic chemistry. Part XVIII. Thermally induced isomerisation of 3-p-alkoxyphenyl-5-methoxyisoxazoles in aryl aldehydes and dehydration of 5-amino-3,4-diarylisoxazoles in hexamethylphosphoric triamide

Abstract

3-p-Alkoxyphenyl-5-methoxyisoxazoles (1), when heated in an aryl aldehyde under reflux, yield 4′-alkoxybenzanilides (5) through isomerisation of the initially produced methyl 3-p-alkoxyphenyl-2H-azirine-2-carboxylate (2) to a ketenimine (3). In addition, isomerisation to 2-p-ethoxyphenyl-5-methoxyoxazole (4; Ar¹=p-EtOC₆H₄) was observed for the isoxazole (1; Ar¹=p-EtOC₆H₄). 5-Amino-3,4-diarylisoxazoles (7), when heated in hexamethylphosphoric triamide under reflux, undergo dehydration via 2,3-diaryl-2H-azirine-2-carboxamides (8), producing 2-arylindole-3-carbonitriles (11) as the major product.