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>Tyinga Molecular Overhand Knot of Single Handednessand Asymmetric Catalysis with the Corresponding Pseudo-D3-Symmetric Trefoil Knot
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Tyinga Molecular Overhand Knot of Single Handednessand Asymmetric Catalysis with the Corresponding Pseudo-D3-Symmetric Trefoil Knot
We report the stereoselective synthesis of a left-handed trefoil knot from a tris(2,6-pyridinedicarboxamide) oligomer with six chiral centers using a lanthanide(III) ion template. The oligomer folds around the lanthanide ion to form an overhand knot complex of single handedness. Subsequent joining of the overhand knot end groups by ring-closing olefin metathesis affords a single enantiomer of the trefoil knot in 90% yield. The knot topology and handedness were confirmed by NMR spectroscopy, mass spectrometry, and X-ray crystallography. The pseudo-D3-symmetric knot was employed as an asymmetric catalyst in Mukaiyama aldol reactions, generating enantioselectivities of up to 83:17 er, which are significantly higher than those obtained with a comparable unknotted ligand complex.
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