Dielectrophilic Allenic Ketone-Enabled [4+2] Annulation with 3,3′-Bisoxindoles: Enantioselective Creation of Two Contiguous Quaternary Stereogenic Centers

We introduced a type of allenic ketone as a dielectrophilic C4 synthon in phosphine-mediated reactions. The high electrophilicity of the advanced intermediates created upon phosphine activation empowered the utilization of 3,3'-bis-oxindoles as a two-carbon reaction partner in a highly enantioselective [4 + 2] annulation, allowing for facile creation of spirocyclic bisindoline structures containing two contiguous quaternary stereogenic centers. Synthetic manipulations of the [4 + 2] annulation product led to concise total synthesis of (-)-folicanthine.

Automated summary

In this study, we introduced a new type of allenic ketone as a dielectrophilic C4 synthon in phosphine-mediated reactions, enabling a highly enantioselective [4 + 2] annulation. This strategy allowed for the facile creation of spirocyclic bisindoline structures containing two contiguous quaternary stereogenic centers. Synthetic manipulations of the [4 + 2] annulation product led to concise total synthesis of (-)-folicanthine.