An Azomethine Ylide Approach to Complex Alkaloid-like Heterocycles

The nitrone above is readily available via the intramolecular aza Diels−Alder reaction of an amino acid derived triene in acetic acid. Subsequent treatment of the nitrone in refluxing toluene with substituted actetylenes produced the pictured pyrrole. At lower temperatures a 2,3-dihydroisoxazole, which is the product of a 3 + 2 dipolar cycloaddition, is produced. Upon heating in refluxing toluene the 2,3-dihydroisoxazole is converted to the pyrrole.