Reaction of hydroxylamine with 5-aminooxazoles. A new route to isoxazoles

The nucleophilic attack of hydroxylamine at the 5 position of 2-aryl-4-trifluoroacetyl-5-amino-oxazoles leads to a mixture of stereoisomeric isoxazolines. Dehydration of these isomeric isoxazolines in the presence of trifluoroacetic anhydride gives 3-amino-4-acylamino-5-trifluoromethylisoxazoles. The structures and spectroscopic data of these compounds are discussed.