Organocatalytic Asymmetric Synthesis of 3,3′-Pyrrolidinyl-bispirooxindoles via Michael/<i>N</i>‑Hemiketalization Cascade Reaction between 3‑Aminooxindoles and Isatin-Derived β,γ-Unsaturated α‑Keto Esters

A novel strategy for the construction of 3,3′-pyrrolidinyl-bispirooxindoles through a Michael/N-hemiketalization cascade reaction of 3-aminooxindoles and isatin-derived β,γ-unsaturated α-keto esters was developed. Under mild conditions, a series of 3,3′-pyrrolidinyl-bispirooxindoles were obtained in moderate to good yields with high diastereo- and enantioselectivities by using a cinchona-derived bifunctional squaramide organocatalyst. This work represents the first example using the 3-aminooxindoles for the construction of 3,3′-pyrrolidinyl-bispirooxindoles.