Studies on ketene and its derivatives. XXV. Ring-closure of 3-acetyl-4-hydroxy-6-methyl-1H-2-pyridone oxime and dehydroacetic acid oxime

Abstract

Treatment of 3-acetyl-4-hydroxy-6-methyl-1H-2-pyridone (V) with hydroxylamine gives its oxime (VI) whose treatment with polyphosphoric acid at room temperature results in the Beckmann rearrangement to afford 3-acetamido-4-hydroxy-6-methyl-1H-2-pyridone (VIII). Further heating of VIII with polyphosphoric acid results in its transition to 2, 6-dimethy1-5H-oxazolo[4, 5-c]pyridin-4-one (IX), which is also obtained on heating VI with polyphosphoric acid directly. IX also transits to VIII when left with hydrochloric acid at room temperature, while hydrolysis of IX with heating gives 3-amino-4-hydroxy-6-methyl-1H-2-pyridone (X). Treatment of dehydroacetic acid oxime (XIV) with polyphosphoric acid gives 3-acetamido-4-hydroxy-6-methyl-2H-pyran-2-one (XVI) and 2, 6-dimethyl-4H-pyrano[3, 4-d]oxazol-4-one (XVII), and the latter transits to IX on treatment with ammonia. Marcus and others5) reported that the reaction of XIV and diketene gave its cyclized product, 3, 6-dimethyl-4H-pyrano[3, 4-d]isoxazol-4-one (XV) but re-examination of this reaction showed that the product is a cyclized oxazolo compound (XVII) via the Beckmann rearrangement.