5-(Benzoyloxymethyl)isoxazole-3-carboxylic Acid Ethyl Ester

We describe here the palladium hydrogenation of ethyl 5-(benzoyloxymethyl)isoxazole-3-carboxylate. The presence of two reducible sites in the molecule, namely the benzylic-like position and the isoxazole N–O bond, creates a possible competition. The results show that under the applied conditions, ethyl (Z)-2-amino-4-oxo-2-pentanoate is obtained as the only product. Accordingly, a domino process occurs, consisting of deoxygenation to the 5-methylisoxazole derivative followed by reductive opening of the isoxazole ring. The isoxazole substrate was prepared by NaOH-catalyzed cycloaddition-condensation of ethyl nitroacetate and propargyl benzoate in water. Complete characterizations of the isoxazole and Z-enaminone derivatives are reported.