Flash Vacuum Pyrolysis of Some 4-Nitroisoxasoles

Article abstract of DOI:10.1021/jo00392a025

Flash vacuum pyrolysis (FVP) of some 5-alkyl-3-methyl-4-nitroisoxasoles affords 1-nitro-1-cyanoacetone as the only product.A general mechanism is suggested which involves isomerization of the isoxazole to a 1-azirine.A nonclassical reaction of 3-methyl-4-nitroisoxazoles is assumed as a consequence of the electron-withdrawing ability of the nitro group, which precludes ring closure of the nitrile ylide intermediate to the oxazole isomer.The formation of 1-nitro-1-cyanoacetone by FVP of the 3-unsubstituted 5-methyl-4-nitroisoxazole suggests that the activation barrier for a 1,2-hydrogen shift from a 1-azirine or vinylnitrene is lower than that for the formation of nitrile ylide.The FVP of 5-ethyl-3-methylisoxzaole affords 5-ethyl-2-methyloxazole.