Asymmetric Synthesis of Pyrazolone Fused Spirocyclohexeneimines via a Vinylogous Michael/Cyclization Cascade Reaction

Diastereoisomeric pyrazolone-fused spirocyclohexenimines, bearing contiguous all-carbon quaternary and tertiary stereocenters, are readily synthesized for the first time in good to excellent yield (up to 98%) and high enantioselectivity (up to 97% ee) via vinylogous Michael reaction/cyclization cascade reaction of α-arylidene pyrazolones and α,α-dicyanoalkylidenes. The formal [4+2] atom-economical annulation proceeds with commercially available Takemoto's catalyst under mild reaction conditions. Scale-up reaction and post-transformation of the products were also demonstrated. (Figure presented.).