Abstract
AbstractThe synthesis of 10 water‐soluble β‐cyclodextrin‐tagged NHC‐gold(I) complexes is described. Key steps are nucleophilic substitutions, as well as, copper‐(CuAAC)‐ and ruthenium‐(RuAAC)‐catalyzed azide alkyne cycloadditions. Whereas the CuAAC reliably affords 1,4‐disubstituted 1,2,3‐triazoles, the regioselectivity of the RuAAC depends on the structure of the coupling partners. Permethylated cyclodextrin‐tagged NHC‐gold(I) complexes are soluble both in water and in organic solvents. They show excellent catalytic activity and recyclability in cyclization reactions of functionalized allenes and alkynes in bulk water. The enantioselective cycloisomerization of γ‐ and δ‐hydroxyallenes could be achieved with up to 38 % ee. Thus, it is possible to take advantage of the chirality of the cyclodextrin moiety for enantioselective gold‐catalyzed transformations.
Highlights
Organic solvents continue to be the reaction media of choice for transformations of organic substrates, notwithstanding the fact that they are the major source of waste produced by chemists in industry and academia.[1]
In the area of homogeneous gold catalysis, we have demonstrated that both strategies[6,7] lead to highly efficient and recyclable catalysts for various transformations in bulk water
We have demonstrated that the ruthenium-catalyzed azide alkyne cycloaddition (RuAAC) is a suitable method for the coupling of cyclodextrin and imidazolium fragments
Summary
The synthesis of 10 water-soluble β-cyclodextrin-tagged NHCgold(I) complexes is described. Key steps are nucleophilic substitutions, as well as, copper-(CuAAC)- and ruthenium(RuAAC)-catalyzed azide alkyne cycloadditions. CuAAC reliably affords 1,4-disubstituted 1,2,3-triazoles, the regioselectivity of the RuAAC depends on the structure of the coupling partners. Gold(I) complexes are soluble both in water and in organic solvents. They show excellent catalytic activity and recyclability in cyclization reactions of functionalized allenes and alkynes in bulk water. The enantioselective cycloisomerization of γ- and δhydroxyallenes could be achieved with up to 38 % ee. It is possible to take advantage of the chirality of the cyclodextrin moiety for enantioselective gold-catalyzed transformations
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