Total Syntheses of (-)-Minovincine and (-)-Aspidofractinine through a Sequence of Cascade Reactions.

We report 8-step syntheses of (-)-minovincine and (-)-aspidofractinine using easily available and inexpensive reagents and catalyst. A key element of the strategy was the utilization of a sequence of cascade reactions to rapidly construct the penta- and hexacyclic frameworks. These cascade transformations included organocatalytic Michael-aldol condensation, a multistep anionic Michael-SN 2 cascade reaction, and Mannich reaction interrupted Fischer indolization. To streamline the synthetic routes, we also investigated the deliberate use of steric effect to secure various chemo- and regioselective transformations.

Total Syntheses of Dihydroindole Aspidosperma Alkaloids: Reductive Interrupted Fischer Indolization Followed by Redox Diversification.

We report a novel reductive interrupted Fischer indolization process for the concise assembly of the 20-oxoaspidospermidine framework. This rapid complexity generating route paves the way toward various dihydroindole Aspidosperma alkaloids with different C-5 side chain redox patterns. The end-game redox modulations were accomplished by modified Wolff-Kishner reaction and photo-Wolff rearrangement, enabling the total synthesis of (-)-aspidospermidine, (-)-limaspermidine, and (+)-17-demethoxy-N-acetylcylindrocarine and the formal total synthesis of (-)-1-acetylaspidoalbidine.