3-Aryl-5-vinyl-2-isoxazolines and 3-aryl-5-vinylisoxazoles from aryl nitrile oxides and methyl vinyl ketone lithium enolate: Reaction limits and synthetic utility exploitation

3-Aryl-5-hydroxy-5-vinyl-2-isoxazolines were synthesized by reacting aryl nitrile oxides with the lithium enolate of methyl vinyl ketone (MVK) at-78 °C. Fair to good yields are obtained in the case of aryl nitrile oxides bearing electron-withdrawing groups on the aryl moiety or less bulky groups. Conversely, lower yields or no reaction was observed in the presence of hindered aryl nitrile oxides. Such a behavior was confirmed by ab initio calculations of the activation energies for three reactions. A number of 3-aryl-5-vinylisoxazoles were quantitatively obtained by dehydration/aromatization of the corresponding 5-hydroxy-2-isoxazolines under acidic conditions. The side-chain elaboration is reported as a synthetic utility of some vinylisoxazoles and vinylisoxazolines