Benzimidazolium- and Benzimidazolilydene-Capped Cyclodextrins: New Perspectives in Anion Encapsulation and Gold-Catalyzed Cycloisomerization of 1,6-Enynes.

A new way of introducing a N-heterocyclic carbene cap onto cyclodextrins has been devised. The benzimidazolium intermediates were found to behave as receptors towards cavity matching anions. The corresponding C1 - and C2 -symmetrical regioisomeric carbene gold(I) complexes have been tested in a benchmark asymmetric cycloisomerization of 1,6-enynes. Up to 50 % ee was achieved for the enantioselective cycloisomerization of N-allyl-4-methyl-N-(3-phenylprop-2-yn-1-yl)benzenesulfonamide.