Synthesis of alpha-cyclodextrin [2]-rotaxanes using chlorotriazine capping reagents.

Ten alpha-cyclodextrin [2]-rotaxanes have been prepared with alkane-, stilbene- and azobenzene-based axles, capped through nucleophilic substitution of either 2-chloro-4,6-dimethoxy-1,3,5-triazine or 2,4-dichloro-6-methoxy-1,3,5-triazine in aqueous solution, followed by further substitution of the remaining triazinyl chlorine in some cases when the latter capping reagent was used. In one case the rotaxane is a [c(2)]-daisy chain obtained by double-capping the corresponding hermaphroditic cyclic dimer. One of the rotaxane azobenzene derivatives was shown to undergo photochemically-induced reversible interconversion between its trans- and cis-isomers, causing the cyclodextrin to move back and forth along the axle, and therefore behave as a molecular shuttle. The methodology is therefore shown to constitute a general and versatile approach for the construction of supramolecular species as the basis of photochemical molecular devices.