The reaction of (chlorocarbonyl)phenyl ketene, with readily available benzhydroxamic acid derivatives, such as benzhydroxamic acid, 4-chlorobenzhydroxamic acid, 3-nitrobenzhydroxamic acid, 4-methylbenzhydroxamic acid, N-hydroxy-3-oxo-3-phenylpropionamide, N-hydroxy-2-phenylacetamide, affords isoxazolone derivatives in high yields in a one step procedure. The formation of the products proceeds by a mechanism, that involves replacement of chlorine of the ketene, by benzhydroxamic acids, followed by rapid ring closure of this intermediate to form isoxazolone derivatives.