High yielding template-directed syntheses of [2]rotaxanes

Three dumbbell-shaped compounds incorporating terminal triisopropylsilyl stoppers, connected to a central 1,5-dioxynaphthalene recognition site by [-CH₂CH₂O-]_n spacers (n = 1-3), have been synthesized. These compounds have been employed as templates for the synthesis of [2]rotaxanes incorporating cyclobis(paraquat-p-phenylene) as the ring component. It was found that the length of the polyether chains of the templates influences the efficiencies of the template-directed syntheses. Rotaxane formation occurs only if n > 1 and, when n = 3 the corresponding [2]rotaxane can be isolated in a yield as high as 72 %. This remarkable yield is the highest ever obtained for the template-directed syntheses of [2]rotaxanes incorporating donor/acceptor Interactions.