Diaryl Crown Ethers And Crown Ethers, Diaryl-based Rotaxane Assembly

Crown ethers are an interesting class of compounds which have spawned the new areaof supramolecular chemistry. As a result, several interesting new classes of moleculesincluding cryptands, rotaxanes, polyrotaxanes, and catenanes have been made. Amongthem, rotaxanes and catenanes attract scientist's great research interest becauserotaxane/catenane-based molecular machines are of great potential uses for thedevelopment of nanoelectromechanical systems (NEMS), such as molecular devices andnano/microrobots, for medicine and everyday-life pursuits.Bisarylene crown ethers are important building blocks for supramolecular chemistryand widely used to build up rotaxanes, catenanes and related molecular machines. Althoughseveral methods have been developed for preparation of bisarylene crown ethers, thesynthetic efficiency is very low (less than 10％). We have now devised a general one-stepapproach to bisarylene crown ethers via pseudo-high dilution and template-directed method.This method allows us have prepared 10 symmetric and 4 unsymmetric bisarylene crownethers. The synthetic yields via such a one-step method, arranging from 20％to 50％, aresatisfactory and 3-5 folds higher than that of reported in literature. The syntheses ofbisarylene crown ethers are carried out in DMF at 100℃by condensation of the ditosylateof tri/tetraethylene glycol with corresponding dihydroxyarylene derivatives. The reactionutilized tetra-n-butylammonium iodide (TBAI) as a phase transfer catalyst and CsF/Cs₂CO₃as the base; pseudo-high-dilution conditions were achieved by interval addition of the twoorganic substrates.Of particular interest to us is the use of bisarylene crown ethers in construction ofnovel rotaxanes and related molecular machines. Having these crown ether building blocksin hands, we turn our focuses to the formation of rotaxanes. Because the reaction betweenprimary alcohol and isoyanate is reportedly quantitative under mild conditions, employingthis method, we have prepared [2]rotaxane 38 and 39, and [3]rotaxane 40 both in solutionand in solid-state. Gratifyingly, the yield of rotaxane formation in solid-state is much higher than that in solution though the reaction transformation in solid-state is a little bit low.In conclusion, we have developed an efficient one-step pseudo-high dilution andtemplate-directed method for the preparation of bis(p-phenylene)-34-crown-10 and itshomologues. We also demonstrated the ease of reaction between primary alcohol andisoyanate for rotaxane formation both in solution and in solid-state.