Efficient One-Pot Synthesis of β -Unsaturated Isoxazol-5-ones and Pyrazol-5-ones Under Ultrasonic Irradiation

4-Arylmethylidene-3-isopropylisoxazol-5-ones and 4-arylmethylidene-1-phenyl-3-isopropylpyrazol-5-ones have been prepared from the reactions of hydroxylamine and phenylhydrazine with methyl 4-methyl-3-oxovalerate and aromatic aldehydes in an aqueous medium at room temperature in the presence of pyridine under ultrasonic irradiation. The simple and facile method produced products in good yields. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.