Bifunctional Squaramide-Catalyzed Asymmetric [3 + 2] Cyclization of 2-(1-Methyl-2-oxoindolin-3-yl)malononitriles with Unsaturated Pyrazolones to Construct Spirooxindole-Fused Spiropyrazolones

The present paper reports a highly stereoselective synthesis of spirooxindole-fused spiropyrazolones through the asymmetric [3 + 2] cyclization reaction of 2-(1-methyl-2-oxoindolin-3-yl)malononitriles with unsaturated pyrazolones under mild conditions. With only a 1 mol % bifunctional squaramide catalyst, a series of chiral dispirocyclic pyrazolone derivatives were attained in high yields (85-97%) with excellent stereoselectivities (up to >99% ee and in all cases >20:1 dr). Moreover, gram-scale synthesis and further transformation of the products were also demonstrated.