Phosphine-Catalyzed Divergent γ,γ- and ε,γ-Umpolung Domino Additions of Bisoxindoles with Allenoates: Construction of Vicinal All-Carbon Quaternary Stereocenters and Formal Total Synthesis of Dimeric Cyclotryptamine Alkaloids

Abstract

Vicinal all-carbon quaternary stereocenters are widely present in natural products and bioactive molecules. However, the construction of such motif in one step from readily available starting materials remains a significant challenge. Herein, we report a phosphine-catalyzed divergent γ,γ- and ε,γ-umpolung domino addition of bisoxindoles with allenoates. This method serves as a practical tool for the concise synthesis of a series of bisoxindole derivatives bearing sterically hindered vicinal all-carbon quaternary stereocenters under mild reaction conditions. The applicability of this novel method was demonstrated with the gram-scale synthesis of three known advanced intermediates for the total syntheses of calycanthine, chimonanthine and folicanthine.