Base‐Mediated Intramolecular Diels–Alder Reaction of Ugi‐Propargyl Adduct: An Efficient Route to Synthesize Highly Substituted Strained 5,9b‐Ethenobenzo[ e ]Isoindoles

ABSTRACT The present work describes a two‐step synthesis of polycyclic 5,9b‐ethenobenzo[e]isoindoles by post‐modification of Ugi‐propargyl adducts. The procedure includes Ugi‐4CR with various aromatic/aliphatic acids, propargylamine, isocyanides, and 1‐naphthaldehyde as carbonyl components to afford Ugi‐propargyl adduct. The Ugi‐propargyl‐adduct underwent base‐mediated in situ conversion of propargyl to N ‐(allenyl)amide functionality, which concurrently led to the regioselective intramolecular Diels−Alder reaction with the naphthyl group to furnish a strained polycyclic 5,9b‐ethenobenzo[e]isoindoles adduct. Evidence for the structures relies on analytical investigations and X‐ray crystallography.