Three-Component Synthesis of Isoxazolone Derivatives in the Presence of 4-(N,N-Dimethylamino)pyridinium Acetate as a Protic Ionic Liquid

The preparation of 3-methyl-4-arylmethylene-isoxazol-5(4H)-ones through three-component reaction of ethyl acetoacetate, hydroxylamine and aromatic aldehydes in the presence of catalytic amounts of 4-(N,N-dimethylamino)pyridinium acetate as a protic ionic compound is described. The reactions proceeded to completion at 70 °C under solvent-free conditions. The reaction of aromatic aldehydes carrying electron-donating groups proceeded rapidly with excellent, isolated yields of the corresponding isoxazolone derivatives. On the other hand, those carrying deactivating groups provided the corresponding products in moderate to high yields. However, this method has the generality for structurally different aromatic aldehydes. By this method, the corresponding products are obtained simply by dilution of the reaction mixture with water and filtration in almost pure crystalline form. The recyclability of 4-(N,N-dimethylamino)pyridinium acetate was also explored and it was observed that this ionic compound can be recycled and reused without appreciable loss in its catalytic activity during six consecutive runs.