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American Chemical Society, Journal of the American Chemical Society, 40(138), p. 13159-13162, 2016

DOI: 10.1021/jacs.6b08421

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Tying a molecular overhand knot of single handedness and asymmetric catalysis with the corresponding pseudo-D3-symmetric trefoil knot

Journal article published in 2016 by Guzmán Gil-Ramírez, Steven Hoekman, Matthew O. Kitching ORCID, David A. Leigh, Iñigo J. Vitorica-Yrezabal ORCID, Gen Zhang
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

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.