Formation of Pyridines by the Reaction of Isoxazoles with Enamines

The reaction of isoxazoles with enamines, proceeded easily to give pyridine derivatives. For example, 1, 2, 3, 4 -tetrahydroquinoline was obtairKedb y the reaction of isoxazole with 1-(1cyclohexenyl)pyrrolidinei n THF or in dioxane under reflux in the presence of low-va lence titanium salt (prepared from titanium(IV) chloride and zinc dust) (yield: 75%). Similarly, various 3(and/or 2)-substituted pyridines were obtained from isoxazoles and β(and/or α)substituted enamines.5-Methylisoxazoles, however, gave pyridines in only poor yields.