From a,fi-unsaturated ketones and hydroxylamine

The first isolated isoxazoline was obtained by this method in 1895, and it has been found to be a highly complicated reaction which yields a variety of products depending on, among other conditions, the pH, concentration, temperature and solvent 62HC(l7)l). 

The reaction of a dibromochalcone with hydroxylamine hydrochloride in pyridine gave three products with the expected 2-isoxazoline product as the predominate compound. A ring bromination product and an isoxazole were also isolated (70UC796). The reaction of hydroxylamine with /S-thiosulfates of propiophenone at reflux produced 3-phenyl-2-isoxazo-line (455). At room temperature a bis-Michael product (456) was produced. The reaction with N -phenylhydroxylamine yielded a mono-Michael type product (457) (74CPB1990). 

Reacting hydroxylamine with the corresponding trichloro derivative (462) under acidic conditions gave an oxazinone (463) while under basic conditions the 2-isoxazoline (464) was produced (80ZC19). 

The action of benzoylmethylides (471) and (472) with nitrosyl chloride produced the 2-trans products (473) and (474) (72T3845). 

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