Cyclodextrin-Catalyzed Diels–Alder Reaction for the Syntheses of Cyclodextrin Polyrotaxanes, Molecular Tubes, and Molecular Shuttles

The existing synthesis methods of cyclodextrin (CD) polyrotaxanes (PRs) are generally tedious and low-yield. Herein, we report an efficient synthesis strategy for α-, β-, and γ-CD PRs. A Diels–Alder (DA) reaction between 9-anthracenemethanol and maleimide was used as the capping reaction since the adduct was large enough to lock α- and β-CDs and the reaction could be catalyzed by CDs, achieving high yields in aqueous medium under mild conditions. For the synthesis of γ-CD PRs, we introduced maleimide-modified second-generation polylysine dendrons at both ends of the polymer axle to slow the dethreading during the capping reaction and increase the number of the end-capping groups. Through the microwave-assistant retro-DA reaction, we synthesized α-, β-, and γ-CD molecular tubes with desirable yields. We further expanded the strategy to the synthesis of β-CD rotaxane-based molecular shuttles and achieved fluorescence modulation using the light-driven shuttle movement of the CD ring along the axle.