Kinetic Evidence for the Intermediacy of 1-Azirines in the Gas-Phase Thermal Isomerization of 3H-Isoxazoles to α-Carbonylacetonitrile Derivatives

Article abstract of DOI:10.1021/jo00345a017

Thermal isomerization of 5-methylisoxazole and 5-amino-4-methylisoxazole to acetylacetonitrile and 2-cyanopropionamide, respectively, was studied in a flow system.The activation parameters are reported.According to the experimental results, a concerted 1,3 sigmatropic shift to 1-azirines is proposed as the rate-limiting step in these reactions.A general reaction mechanism for the isomerization of isoxazoles into 1-azirines, oxazoles, and α-carbonylacetonitrile derivatives is discussed.