Phosphine-Catalyzed Sequential [3 + 2]/[3 + 2] Annulation between Allenoates and Arylidenemalononitriles for the Enantioselective Construction of Bicyclo[3,3,0]octenes and Cyclopenta[c]quinolinones

A highly diastereo- and enantioselective phosphine-catalyzed sequential [3 + 2]/[3 + 2] annulation of allenoates with arylidenemalononitriles has been developed. This reaction allows for the facile construction of multifunctionalized cis-fused bicyclic[3,3,0]octene scaffolds, encompassing three consecutive stereogenic centers with one quaternary carbon center, in a one-step operation from readily available materials. The reported protocol is scalable, operates under mild reaction conditions, and creates the core structural motif of a number of natural products.