A general method for the synthesis of bridged indole alkaloids

Abstract

The nucleophilic addition of indoleacetic ester enolates to pyridinium salts, followed by acid-promoted cyclization of the intermediate 1,4-dihydropyridines, leads to tetracyclic substructures of C-mavacurine, Strychnos, and akuammiline alkaloids. Further closure of the tryptamine chain by cyclization upon the indole nucleus has completed total syntheses of pentacyclic C-mavacurine and Strychnos alkaloids. The extension of the methodology to the synthesis of alkaloids having other skeletal types (akagerine, ervitsine) from 1- or 2-acetylindoles is also discussed.