Phosphine-Catalyzed (3 + 2)/(3 + 2) Sequential Annulation of γ‑Vinyl Allenoates: Access to Fused Carbocycles

The first (3 + 2)/(3 + 2) sequential annulation of γ-vinyl allenoates with alkylidenemalononitriles enabled by phosphine catalysis has been reported. A broad range of structurally dense tetra- and penta-substituted bicyclic­[3,3,0]­octene derivatives, containing a quaternary center and three sequential stereogenic center, were synthesized in good to excellent yields. In this approach, three new C–C bonds are formed in one pot, and εC and αC of γ-vinyl allenoate are two electrophilic centers, whereas its γC exhibits nucleophilic reactivity.