Enantioselective 1,3-dipolar cycloaddition of methyleneindolinones and N,N′-cyclic azomethine imines

Abstract

A new chiral bis-phosphoric acid 3l bearing triple axial chirality was synthesized and applied to effect a highly enantioselective 1,3-dipolar cycloaddition reaction between N,N′-azomethine imines and methyleneindolinones for the creation of chiral spiro[pyrazolidin-3,3′-oxindoles] in excellent yields and selectivities. MS experiment and DFT calculation studies prompted us to propose a dual H-bond donor activation mode of bis-phosphoric acid which is different from the traditional phosphoric acid catalysis.