CALIXARENES AS STOPPERS IN ROTAXANES

The synthesis of the amide-based rotaxane 7a bearing calix[4]arene blo cking groups is described for the first time. While rotaxane formation fails if a calix[4]arene is functionalized at the upper rim with only an amino or methylamino group lakking any spacer, the prolonged amine 5a works successfully as stopper unit preventing dethreading of the d imeric wheel 1a by its size. Rotaxane formation of 8b was observed onl y by MALDI-TOF mass spectrometry of the reaction mixture of the amine 5b, the axle 6 and la. With the larger trimeric wheel Ib no stable rot axane could be obtained. It either does not act as a concave template or its opening is too wide, even for the bulky calixarene stoppers.