Synthesis of rotaxanes

Schalley CA, WeUandt T, Briiggemann J,V6gtle F (2004) Hydrogen-Bond-Mediated Template Synthesis of Rotaxanes, Catenanes, and Knotanes. 248 141-200 Scheer M,see Balazs G (2003) 232 1-23... 

Template effects have been used in rotaxane synthesis to direct threading of the axle through the wheel. Since macrocycHc compounds such as cyclodextrins, crown ethers, cyclophanes, and cucurbiturils form stable complexes with specific guest molecules, they have been widely used in the templated synthesis of rotax-anes as ring (wheel) components. Here, we briefly discuss macrocycles used in the synthesis of rotaxane dendrimers and their important features. 

In this review, we tried to cover all the supramolecular species that maybe classified as rotaxane dendrimers. We classified them by their structures - where in dendrimer rotaxane-hke features are introduced. Several different types of macrocycles have been employed as a ring component in the templated synthesis of rotaxane dendrimers. While the synthesis of Type I and II rotaxanes dendrimers is relatively straightforward, that of well-defined Type III rotaxane dendrimers, particularly those of second and higher generations, is still challenging. 

Blanco, M.-J., Transition-Metal-Templated Synthesis of Rotaxanes, 23, 125. 

M. Handel, M. Plevoets, S. Gestermann, F. Vogtle, Synthesis of Rotaxanes by Brief Mdting of Whed and Axle Components , Angew. Chem. Int. Ed. Engl. 1997,36,1199-1201... 

Figure B. Pictorial representation of the self-assembly of pseudorotaxa-nes based on (a) charge-transfer and C-H—O hydrogen-bonding interactions between 1,1 -diben-zyl-4,4 -bipyridinium dication and 1,5-dinaphtho[38] crown-10 (1/5DN38C10), and (b) hydrogen-bonding interactions between dibenzyl ammonium ion and dibenzo[24]crown-8 (DB24C8). A possible route towards the synthesis of rotaxanes and catenanes is also schematized.

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... 

The anion-templated synthesis of rotaxanes first introduced by Vogtle has now been employed by others to produce other interlocked assemblies. Schalley for example [68], has reported an improved yield for the synthesis of rotaxanes by... 

Schalley CA, Weilandt T, Briiggemann J, Vogtle F (2004) Hydrogen-bond-mediated template synthesis of rotaxanes, catenanes, and knotanes. Top Curr Chem 248 141-200... 

Diinnwald T, Jager R, Vogtle F (1997) Synthesis of rotaxane assemblies. Chem Eur J 3 2043-2051... 

Hydrogen-Bond-Mediated Template Synthesis of Rotaxanes, Catenanes, and Knotanes... 

Figure 51. Anionic template synthesis of rotaxane 118 with a bis(phenyl ether) axle. The mechanical bond is formed by reaction of the phenolate-macrocycle complex [32-115] (supramolecular nucleophile) with the semiaxle intermediate 117. 

Figure 10.56 Synthesis of rotaxanes via self-assembly of electron-rich and electron-poor aryl fragments. (Reproduced with permission from [58]).

Figure 1. Different template strategies a) Metal ions, b) 7t-acceptor ft-donor interactions and c) hydrogen bonding mediate the template synthesis of rotaxanes.

The amide-based template synthesis of rotaxanes, catenanes and knots were first discovered by Vogtle and coworkers when they tried to synthesize macrocycle 3 [13], The cyclization to yield the tetralactam ring was carried out under high-dilution... 

Fig. 14 Principle of the synthesis of rotaxane 16 +(see Figure 15). (i) Formation of a monostoppered axle, (ii) Threading ofthe axle through the wheel, (iii) Unthreading ofthe macrocycle is prevented by adding a second blocking group.

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 choice of one of these four routes for the preparation of a rotaxane depends mainly on the chemical nature of the different components and the chemistry required to establish the interlocked molecule. An interaction between the two individual components is very often the driving force in the synthesis of rotaxanes. 

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