A new approach to cyclodextrin-based rotaxanes
A new synthetic strategy for the preparation of cyclodextrin-based rotaxanes is described. The method is essentially based on the formation of stable inclusion complexes between a-CD and aliphatic chains. The interaction in aqueous media of compounds containing a long alkyl chain terminated in a bulky (ferrocenylmethyl)dimethylammonium group with a-CD leads to inclusion complexes in which the cyclodextrh is threaded by the alkyl chain. Functionalization of the other chain terminus with a wboxylic acid group allows trapping of the chain-threaded CD receptor via amidation reactions of the carboxylic functional group with bulky amines. The rotaxane products are asymmetric since the two terminal groups are different. This feature allows, for the first time, the detection of isomeric rotaxanes exhibiting the two possible orientations of the trapped CD.