Studies in isoxazole chemistry. II. Isoxazoles from the Δ2-isoxazolin-5-ols and their acetates

Various 3-substituted-5-acetoxy-Δ2-isoxazolines were made by the 1,3-dipolar cycloaddition of nitrile oxides to vinyl acetate or isopropenyl acetate. These compounds were readily converted in high yield to 3-substituted isoxazoles or 3-substituted-5-methylisoxazoles respectively, on heating. Treatment of the 3-substituted-5-acetoxy-Δ2-isoxazolines with sodium hydroxide in methanol gave rise to the stable Δ2-isoxazolin-5-ols after acidification. These compounds could also be converted to 3-substituted isoxazoles by heating alone, or better, in the presence of thionyl chloride. The nuclear magnetic resonance spectra of these compounds are discussed.