Studies on the Synthesis of the Alkaloid (-)-Gilbertine via Indolidene Chemistry.

A synthesis route to the pentacyclic alkaloid (-)-gilbertine, which features a cyclization cascade passing through a transient indolidene intermediate, was pursued. A key stereochemical relationship was set via a Nicholas-type enolate alkylation. Ultimately, undesired C-N cyclization thwarted the final projected C-C bond forming ring closure, and gilbertine could not be prepared by this route.