125 / 2023-10-12 10:33:13

Phosphine-Catalyzed Asymmetric Dearomative [3+2] Annulation Reaction of Benzimidazoles with Cyclopropenones

Chiral phosphine; Asymmetric catalysis; Dearomatization; Cycloaddition

Phosphorus in Synthetic Chemistry > 1) Phosphorus compounds as catalysts

Aromatic compounds are important structural motifs and widely distributed in nature. Among them, heterocyclic aromatics, especially those containing one or more nitrogen atoms, occupy a privileged position as they are found in numerous biologically active compounds and pharmaceuticals.^[1] Catalytic asymmetric dearomatization (CADA) reactions recently received great attention as they provided a direct access to enantioenriched three-dimensional molecules from simple planar aromatic compounds.^[2] Compared with the well-studied reactions involving electron-rich heteroarenes, the CADA reactions of electron-deficient heteroarenes remain relatively limited. Benzimidazoles, benzoxazoles, and benzothiazoles are important electron-deficient heterocyclic aromatics, and only a few examples of CADA reactions catalyzed by metal have been reported.^[3] However, the reaction catalyzed by organocatalysts has not been reported. Therefore, it remains essential to further develop different catalytic systems for the electron-deficient heteroarenes.

Herein, we report a phosphine-catalyzed intermolecular asymmetric dearomatization reaction of benzimidazoles with cyclopropenones. Through this method various of dearomatized heterocycle products were obtained in high yield (up to 98%) and excellent enantioselectivity (up to 99% ee). Meanwhile, this reaction features mild reaction conditions and excellent functional group tolerance.