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.