Divergent Total Syntheses of Aspidospermidine, N-Methylaspidospermidine, N-Acetylaspidospermidine and Aspido-spermine via a Tandem Cyclization of Tryptamine-Ynamide

The divergent total syntheses of aspidospermidine, N-methylaspidospermidine, N-acetylaspidospermidine and aspidosperm-ine were achieved from a common pentacyclic indoline intermediate. The common pentacyclic indoline intermediate was synthesized on a gram scale through a Stork-type alkylation of 1H-pyrrolo[2,3-d]carbazole derivatives, which was prepared based on a Brønsted acid-catalyzed tandem cyclization of tryptamine-ynamide. Scalable synthesis of 1H-pyrrolo[2,3-d]carbazole afforded a facile access and practical approach to the Aspidosperma indole alkaloid family.