Ring transformations in reactions of heterocyclic compounds with nucleophiles (VIII). Conversion of pyrimidines into isoxazoles

When pyrimidine, 1‐methylpyrimidinium methosulfate, 1,3‐diethylpyrimidinium tetrafluoroborate or pyrimidine N‐oxide is reacted with hydroxylamine hydrochloride, isoxazole is formed in a good yield. On reaction of 4,6‐dimethylpyrimidine and its corresponding N‐oxide with the same reagent 3,5‐dimethylisoxazole is obtained. Similarly, from 6‐methyl‐4‐phenylpyrimidine 1‐oxide 3‐methyl‐5‐phenylisoxazole is formed. It has been found by 15N‐labelling experiments that the NO moiety of the isoxazole ring originates from the hydroxylamine and not from the magnified image function of the pyrimidine N‐oxide.