Capping rotaxane synthesis

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... 

Figure 11.7 Three strategies for rotaxane synthesis capping, dipping and slipping...

Scheme 13 Templated synthesis of rotaxane 22 employing the threading-followed-by-capping methodology...

Scheme 15 Templated synthesis of rotaxane 24 employing the threading-followed-by-capping methodology. The shift of the proton from the terminal amine to the secondary amine allows for the threading to occur yielding the pseudorotaxane 26... 

Scheme 20 Synthesis of [2] rotaxane 45 by a three-component threading-followed-by-capping mechanism...

Gassensmith JJ, Barr L, Baumes JM, Paek A, Nguyen A, Smith BD (2008) Synthesis and photophysical investigation of squaraine rotaxanes by clicked capping . Org Lett 10 3343-3346... 

For the preparation of rotaxanes, three different routes can be followed (Scheme 6.2A). In the threading procedure, the macrocycle will first encircle the thread to form a so-called pseudorotaxane. By end-capping the thread with bulky groups that prevent de-threading, a [2]rotaxane is formed. The clipping method that is used for the preparation of catenanes can also be applied for the synthesis of rotaxanes hence the macrocycle is assembled in the presence of the end-capped... 

The first mention of synthetic rotaxanes appeared in 1967 [11]. It was based on statistical threading of an immobilized cycle by decane-1,10-diol followed by capping using a trityl ether bulky oup. Another system using statistical threading 1 to rotaxanes in relatively high yield [12]. A directed synthesis was also reported in 1969 by Schill and Zollenkopf.[13]... 

Recently, Leigh et al. [189] prepared the [2]rotaxane 74 by the Cu-mediated Cadiot-Chodkiewicz active-metal template strategy (Scheme 9.25). The mechanically interlocked structure 74 was obtained in a high yield on crosscoupling of the bromoacetylene 75 with the terminal alkyne 76, both of which contained bulky end-capping groups. The cmdal step in the synthesis of 74 was... 

Harada et al. [18] reported the synthesis of a [2]rotaxane capped by j6-CD and a trinitrophenyl group. The /i-CD at the end binds the trinitrophenyl group stopper of another [2]rotaxanes gives a rotaxane aggregate, as shown in Fig. 2. Liu et al. [19] also developed a simple strategy to prepare polyrotaxane-like supramolecules. An inclusion compound had been synthesized by the complexation of 4,4 -di-pyridine and j6-CD in water the subsequent coordination of the complex with nickel ions in aqueous solution gave the corresponding pseudopolyrotaxane. 

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