A Facile Synthesis of 3,4-Disubstituted Isoxazole Derivatives by Regioselective Cleavage of Pyrano[3,4-C]Isoxazoles with Boron Trihalide

Abstract

4,5-Dihydro-7H-pyrano[3,4-c]isoxazoles 4 were efficiently prepared by the intramolecular nitrile oxide-alkyne cycloaddition following the Michael addition of sodium alkoxide to nitroalkene. Reaction of pyrano[3,4-c]isoxazole 4 with boron trihalide resulted in regioselective benzylic C-O bond cleavage to furnish a 3,4-disubstituted isoxazole (5, 6) in high yield.