ChemCatChem
10.1002/cctc.201901658
FULL PAPER
solubility of permethylated cyclodextrin derivatives both in water
and in organic solvents is a huge benefit for these applications.
Keywords: cyclodextrins • gold catalysis • green chemistry •
click reactions • recyclable catalysts
*
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In this paper, the synthesis of 10 β-cyclodextrin-tagged NHC-
gold(I) complexes and their application in cyclization reactions of
unsaturated substrates both in organic solvents and in water are
described. Key structural features of these complexes are a tether
of variable length and flexbility between the cyclodextrin and
NHC-gold moiety, as well as, different steric properties at the
N-heterocyclic carbene. The coupling between the fragments was
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1
15
the aid of H- N-HMBC spectra. The new β-cyclodextrin-tagged
NHC-gold(I) complexes show excellent catalytic activity and
recyclability in cyclization reactions of functionalized allenes and
alkynes in bulk water. Moreover, enantioselective cycloisomeriza-
tions of γ- and δ-hydroxyallenes could be achieved with up to 38%
ee, taking take advantage of the chirality of the cyclodextrin
moiety. Further work is devoted to the fine-tuning of CD-tagged
NHC-gold catalysts by variation of the size and substitution
pattern of the cyclodextrin, as well as, the complexation properties
of the complexes, including the possibility of self-complexation.
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Experimental Section
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Experimental Details are given in the Supporting Information.
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Acknowledgements
We thank Matthias Mawick for experimental assistance.
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