Total Syntheses of Aspidospermidine, -Methylaspidospermidine, -Acetylaspidospermidine, and Aspidospermine via a Tandem Cyclization of Tryptamine-Ynamide.

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