A general method of synthesis of 4-isoxazolones from $\beta$-diketones is reported via the cloroderivatives of the latter, followed by treatment with sodium acetate and hydroxilamine. 3, 5-diphenyl, 3, 5-dimethyl, 3, 5-diethyl and 3-phenyl-5-methyl-4-isoxazolones are so synthesized. Some intermediates such as mono- and di-oximes are isolated, depending on the reaction conditions. 3, 5-diphenyl and 3, 5-dimethylisoxazolones appear to exist in two polymorphic forms, with different melting points (105° and 125° the former, 83° and 94° the latter). The U.V. spectra of all the isoxazolones synthesized, both in ethanol and in KOH, are reported.