Synthesis of isoxazole-5-(4H)-one derivatives 3a–k in the presence of Fe₃O₄@chitosan–SO₃H^a,b.

^aIsolated yield.

^bThe reactions were carried out with 1a–c (1 mmol), β-keto ester 2 (1.5 mmol), hydroxylamine hydrochloride (1.5 mmol) in ethanol or water (10 mL) at room temperature.