Synthèse d'isoxazoles substitués en α de l'azote par une chaine alkyle ou alcényle

Abstract

Several syntheses of special isoxazoles bearing a long alkyl or alkenyl side chain in the α position of the nitrogen are presented. A very convenient route in the case of an alkyl side chain is the classical 1,3-dipolar cycloaddition of a nitrile-oxide to a vinyl acetate. Although it is a rather long approach, the reaction of hydroxylamine with enone-epoxides represents a new and unequivocal method compatible with alkenyl side chains. The isomerisation of the easily synthesized isoxazoles bearing such substitutents α to the oxygen, by the reaction of their isoxazolium salts with hydroxylamine, is a fast and general method. Another very convenient access to "α-N substituted" isoxazoles is the coupling of magnesium compounds with 3-bromomethyl 5-methyl isoxazole. Keywords: isoxazoles, substitution in the α position of nitrogen.