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.