Syntheses with isoxazoles; the production of an isoxazolo[2,3-a]pyridinium salt, and the photochemical conversion of isoxazole-3-carboxylates into oxazole-2-carboxylates

Abstract

Cyclisation of 3-(4-ethoxybutyryl)isoxazole (6) gave 4,5,6,7-tetrahydro-4-oxoisoxazolo[2,3-a]pyridinium bromide (7). An attempt to aromatise the ketone (7) with boiling acetic anhydride was unsuccessful, but bromination gave a dibromo-ketone (9), which was dehydrobrominated to 5-bromo-4-hydroxyisoxazolo[2,3-a]pyridinium bromide (10). The photochemical conversion of isoxazole-3-carboxylates into the corresponding oxazole-2-carboxylates is described.