Cyclodextrin-Based Size-Complementary [3] Rotaxanes: Selective Synthesis and Specific Dissociation

alpha-Cyclodextrin (CD)-based size-complementary [3] rotaxanes with alkylene axles were prepared in one-pot by end-capping reactions with aryl isocyanates in water. The selective formation of [3] rotaxane with a head-to-head regularity was indicated by the X-ray structural analyses. Thermal degradation of the [3] rotaxanes bearing appropriate end groups proceeded by stepwise dissociation to yield not only the original components but also [2] rotaxanes. From the kinetic profiles of the deslippage, it turned out that the maximum yield of [2] rotaxane was estimated to be 94 %. Thermodynamic studies and NOESY analyses of such rotaxanes revealed that [2] rotaxanes are specially stabilized, and that the dissociation capability of the [3] rotaxanes to the components can be adjusted by controlling the structure of the end groups, direction of the CD groups, and length of the alkylene axle.