Rotaxane structure synthesis

The rotaxane is composed of a glycylglycine chain, a simple dipeptide, bearing two diphenylmethane blocking groups, which prevent the dethreading of the benzylic amide macrocycle. The synthesis of the rotaxane structure is based on... 

Synthesis of metal-free rotaxane Structure 28 (PF6 ) (Scheme 9.21)... 

Template synthesis and chirality of catenanes, rotaxanes, and pretzelanes including N-macroheterocyclic lactams and related compounds as structure components 99PAC247. 

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. 

Rotaxanes are the compounds consisting of noncovalent entities called rotor and axle [77], Figure 21 illustrates them schematically. Initially, attempts were made to prepare them by statistical methods, so that the yields were necessarily very low [78-80], Recently, methods have been proposed for their more efficient synthesis, with renewed interest in their unique structure and properties. Section 4.1 summarizes some of the typical results obtained. 

A useful summary of the various and numerous types of rotaxanes, catenanes, and knots can be found in a review of template routes to interlocked molecular structures 468). Inorganic chemistry is centrally involved in the templating involved in self-assembly and in controlled synthesis of such species. 

An overview of the synthesis, structure, photophysical properties, and applications of squaraine rotaxanes as fluorescent imaging probes and chemosensors is provided in a recent review [67]. Although a variety of squaraine dyes form rotaxanes with the molecular cage 25 or with a tetralactam macrocyclic system introduced by Leigh and co-workers [16, 17], there is no evidence in the literature that conventional cyanine dyes can be embedded in these macrocycles. 

Figure 30. The threading synthesis of [2]rotaxanes tolerates the expansion of the cavity and the alteration of the structure of the sulfonamide wheel 65.

To overcome the low yields encountered in statistical methods, Schill and coworkers imaginatively introduced the chemical conversion method [4, 5, 16]. As illustrated in Figure 2, this method requires very careful design (i) the cavity of a cyclic species covalendy linked to a difunctional linear species should be penetrated by the linear species, structure 14 and (ii) both the cyclic and the linear moieties must be inert to the cleavage reaction of the covalent linkage Z between them. By this means, the yield for rotaxane synthesis was increased to about 40% in last step. The disadvantages of this method are its multiple steps and time-consuming nature. 

Inorganic templating and self-assembly provide coordination compounds whose geometries make possible the synthesis of complex structures, namely of cyclic multiporphyrin arrays [9.13a, 9.179], of inorganic rotaxanes [9.97a, 9.180], of multi-catenates and catenands (see 181) [8.281, 8.282] and even of molecular knots (see 182) [8.282, 9.77, 9.181] (in 181 and 182 a) with, b) without Cu(l) template). 

Yamaguchi, I., Osakada, K., Yamamoto, T., Polyrotaxane containing a blocking group in every structural unit of the polymer chain. Direct synthesis of poly(alkylenebenzimidazole) rotaxane from Ru complex-catalyzed reaction of 1,12-dodecanediol and 3,3-diaminobenzidine in the presence of cyclodextrin. J. Am. Chem. Soc. 1996, 118, 1811-1812. 

The functionalisation also allows extending the complexity of intertwined molecular assemblies involving molecular catenanes, rotaxanes and knots. Elaborate interlocked assemblies constructed by means of metal-templation techniques and ji-ji-stacking preorganisation were reviewed [3, 11], Our last survey was devoted to the hydrogen bond templated synthesis of amide-based catenanes and rotaxanes [32], Since then a considerable advancement in elucidation of mechanisms of templation and derivatisation of the amide-based interlocked structures has been reached. Moreover, in 2000 we reported a one pot synthesis of amide-based knots such as 8 [21], which is so far the easiest preparation of molecular knots. In the following, specific possibilities of functionalisation of amide-based catenanes, rotaxanes and knots will be discussed. 

It was not only for the basic scientific knowledge but also for the new challenges in the synthesis and the beauty of the final structures that nearly half a century ago, chemists started to investigate intertwined macrocyclic supramolecules such as rotaxanes and catenanes [4], Earlier, when the syntheses of such structures were at their infancy, the routes to such systems were troublesome. The statistical methods [5] proved to be low-yield processes. Multistep procedures [6] involving a covalent junction which is formed between two parts that are needed to stay together until the structure is complete were not convenient as well. The use of non-covalent templates thus provided a more straightforward and high-yield approach to the problem. 

A successful synthesis of a rotaxane of this type is shown in Figure 5. First, one tiityl aniline stopper is reacted with the terephthaloyl chloride to from semiaxle 9. This semiaxle threads into the tetralactam macrocycle 3 and is held by the amide template. Then, the preorganized complex is reacted with the second stopper 11 to yield rotaxane 12. Figure 5 shows three hydrogen bonds to form, which is in accord with AMI calculations on this system [19] and X-Ray crystal structure analysis [22],... 

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