Organocatalytic Asymmetric Synthesis of 3,3'-Pyrrolidinyl-bispirooxindoles via Michael/ N-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.