Sustainable gold catalysis in water using cyclodextrin-tagged NHC-gold complexes

Abstract

The 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.