Synthesis of tetracyclic indole-containing ring systems by intramolecular cycloadditions of azomethine ylides

Dipolar cycloaddition of azomethine ylides derived from addition of amines to a 2-butenylindole-3-carboxaldehyde provides a stereoselective synthesis of tetracyclic products present in a variety of indole alkaloids. The chemistry was applied to a formal synthesis of the iboga alkaloid deethylibophyllidine.