Phosphine-Catalyzed Sequential [2 +3] and [3 + 2] Annulation Domino Reaction of γ‑Benzyl-Substituted Allenoates with α,β-Unsaturated Ketimines To Construct aza-Bicyclo[3,3,0]octane Derivatives

A novel phosphine-catalyzed sequential [2 + 3] and [3 + 2] annulation domino reaction of γ-benzyl-substituted allenoates has been developed. The reaction can proceed smoothly to produce the corresponding aza-bicyclo­[3,3,0]­octane derivatives in good yields and excellent diastereoselectivity (only one isomer).