Lewis-Base-Catalyzed [1 + 2 + 2] Annulation Reaction of Morita-Baylis-Hillman Carbonates with Unsaturated Pyrazolones: Construction of All-Stereogenic Carbon Cyclopentane-Fused Dispiropyrazolones.

The first Lewis-base-catalyzed unexpected [1 + 2 + 2] annulation reaction between Morita-Baylis-Hillman carbonates and unsaturated pyrazolones was developed. The multicyclic cyclopentane-fused dispiropyrazolone constructions containing five contiguous stereogenic centers, including two spiro quaternary centers, were prepared with excellent yields (81-98%) and moderate to good diastereoselectivities (1:1 to 13:1). Further transformation and gram-scale operations were also achieved efficiently.