Phosphine-Catalyzed Cascade [3 + 2] Cyclization−Allylic Alkylation, [2 + 2 + 1] Annulation, and [3 + 2] Cyclization Reactions between Allylic Carbonates and Enones

The phosphine-catalyzed annulations between Morita−Baylis−Hillman adduct carbonates and enones are reported. Under the catalysis of PBu₃ (20 mol %), cascade [3 + 2] cyclization−allylic alkylation, [2 + 2 + 1] annulation, and [3 + 2] cyclization reactions chemoselectively occur depending on the substituent variation of both the carbonate and enone. These reactions provide efficient syntheses of highly functionalized cyclopentenes and cyclopentanes.