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.
- allenic ketone
- bifunctional phosphine
- quaternary stereogenic centers
- [4 + 2] annulation
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