Reaction conditions were found to allow the exclusive formation of isoxazole-5-carboxylic acid derivatives by conjugate addition, in acidic medium, of hydroxylamine to β-alkoxyvinyl trichloromethyl ketone in synthesis and reactivity of isoxazoles. Isoxazole-5-carboxylic acid participates in the Synthesis and evaluation of acylguanidine FXa inhibitors. 1, 1, 1-trichloro-4-methoxy-3-penten-2-one postulated in the preparation of isoxazole-5-carboxylic acid from trichloroacetyl chloride, ethyl vinyl ether and hydroxylamine is developed in a fully saturated nitrogen atom theerefore there is no possibility of conjugation with 4- substituents.
