Enantioselective Vinylogous Michael-Aldol Reaction To Synthesize Spirocyclohexene Pyrazolones in Aqueous Media.

An efficient asymmetric vinylogous Michael-aldol domino reaction between α-arylidene pyrazolinones and β,γ-unsaturated-α-ketoesters catalyzed by a chiral N, N'-dioxide-ScIII complex in aqueous media has been established. A variety of spirocyclohexene pyrazolones with three stereocenters including vicinal tetrasubstituted stereocenters were obtained in excellent yields with good diastereoselectivities and enantioselectivities. A retro-aldol process was observed, which led to epimerization at the spirocyclic quaternary carbon center.