Synthesis of 3-isoxazolols revisited. Diketene and (β-ketoesters as starting materials

3-Isoxazolols can be made in good yields from β-ketoesters or diketene and hydroxylamine, provided that pH is kept at about 10 throughout the reaction, and that the reaction mixture is quenched with an excess of strong mineral acid. This suppresses the formation of 5-isoxazolones, which are otherwise normally the main products of the reaction.