Rotaxanes oligorotaxanes

Acylation of hydroxy groups of axle components is one of the most effective end-capping methods of rotaxane synthesis. While acylation of alcohol is usually carried out in the presence of tertiary amines such as triethyl-amine, the use of amine significantly decreased the yield of the rotaxane. Takata et al. have demonstrated that the use of the combination of trib-utylphosphine as a catalyst and acid anhydride as an acylation reagent is an excellent solution to this problem [60]. The acid-catalyzed acylation is also effective [61]. The oligorotaxanes were easily prepared in more than... 

In this type of rotaxane, the intramolecular hydrogen-bonding interaction between ammonium salt and crown ether is too strong to neutralize the ammonium part with usual bases. In fact, Takata et al. found that the rate of proton-exchange between [2]rotaxane and water was far slower than that between pyrrole and water, suggesting the extremely lowered acidity of the ammonium moiety [74]. However, the ammonium group can be quantitatively acylated by the excess amount of electrophile in the presence of excess triethylamine. Some oligorotaxanes can be prepared by this process (Scheme 12). 

Cyclophanes are the class of synthetic receptors that have a hydrophobic cavity. Water-soluble cyclophane can make organic compounds soluble in water via the formation of inclusion complex. Anderson et al. synthesized rod-like organic compounds in water in the presence of water-soluble cyclophanes, and obtained corresponding rotaxanes. When oxidative coupling of an acetylenic derivative in the presence of a cyclophane, an oligorotaxane having an axle with a conjugated structure was dominantly obtained rather than non-complexed diacetylene.[187,188] (Scheme 31). This rotaxane is a prototype of insulated molecular wire that is expected as an electric wire in a molecular device. 

Fig. 8 The three families of oligorotaxanes, exemplified by compounds derived from a heptameric DNP thread. The rotaxanes moods depend on their adherence to a selection rule forbidding CBPOT " to occupy adjacent DNP sites. Whereas Confiased rotaxanes can adopt multiple stable translational isomers and Frustrated rotaxanes cannot obey the rule at all, Happy rotaxanes express a single rule-compliant isomer...

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