Phosphine-Catalyzed Asymmetric Dearomative Annulation of 4-Nitroisoxazoles with Allenoates: Construction of Isoxazoline-Fused Bicyclo[3.3.0]octenes.

An intermolecular phosphine-catalyzed dearomatization reaction of 4-nitroisoxazoles with allenoates was realized through one-pot sequential [3 + 2]/[3 + 2] annulation. Various isoxazoline-fused bicyclo[3.3.0]octene derivatives were successfully synthesized in good to excellent yields (up to 98%). Under catalysis with , enantioselective dearomative cyclization occurred, initiating the subsequent [3 + 2] cycloaddition process to afford valuable optically active cyclopentane-fused polycyclic scaffolds bearing a quaternary carbon stereocenter in 58-98% yields with 70-97% ee. The synthetic utility of this protocol was demonstrated by the gram-scale reaction and versatile transformations of the product.