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-3,30-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.
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| http://dx.doi.org/10.1039/c3cc41507d | DOI Listing |
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