One-pot synthesis of tetrahydro-β-carbolines, fused
with
an isoindole core, was proposed starting from maleic anhydride and
azomethines easily available from tryptamines and 3-(hetaryl)acroleins.
This sequence includes four key steps: an acylation of the aldimine
with maleic anhydride, a Pictet–Spengler cyclization, an intramolecular
Diels–Alder reaction, and a concluding [1,3]-H shift. As a result, six- or seven-nuclear alkaloid-like heterocyclic
systems, containing a benzo[1,2]indolizino[8,7-b]indole
fragment annulated with furan, thiophene, or pyrrole, are formed in
a diastereoselective manner.