Isoxazol-5-ones, 4-acyl-, rearrangement

Acylisoxazol-5-ones (129), which are -diketones, on being heated in alkaline medium undergo acyl-lactonic rearrangement to form stable isoxazole-4-carboxylic acids (130). ... 

Oxazoles 240 have also been prepared by flash vacuum pyrolysis or photolysis of A -acylisoxazol-5-ones 239 (Scheme 70) <1996TL675>. The acylisoxazol-5-ones were in turn prepared by the acylation of the corresponding isoxazol-5-ones 238. This method of oxazole production has been reported to give significantly better yields than the rearrangement of the acyltriazole precursors. 

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