Catenanes directed synthesis

As already said, catenanes are minimally composed of two interlocked rings. If it is arranged during the template-directed synthesis to have two identical units, that is, recognition sites, located within two different macrocycles, then the resulting... 

In a directed synthesis, the separate parts of the molecule are held together by other bonds that are later cleaved. See 9-65 for statistical and directed syntheses of catenanes."4... 

Figure 15. The template-directed synthesis of the [2]catenanes 32-4PF6-384PF6. The insets show (i) the intermediate [2]pseudorotaxane formed during the course of catenane formation and (ii) the solid-state structure of the [2]catenane 324+.

Figure 28. The hydrogen-bonding template-directed synthesis of the [2]catenane 87.

There are two distinct approaches to catenane synthesis the statistical approach, and approaches relying on self-assembly, so-called directed synthesis . The statistical approach relies on the small chance that macrocyclisation may occur while a linear precursor is threaded through a macrocyclic component. Because this is a rather unlikely eventuality, it naturally results in low yields of interlinked product and is chiefly of historical interest. It was this kind of statistical approach that resulted in the first synthesis of a [2] catenane by Wasserman in 1960 (10.64), from cyclisation of the long-chain diester 10.65 while threaded through the annulus of a deuterated C34 cycloalkane 10.66 (Scheme 10.11), 57 Although the overall yield of the catenation reaction was less than 1 %, the existence of the catenane was firmly established. The relatively polar [2] catenane product, along with other polar macrocyclisation reaction products and... 

Scheme 10.20 Directed synthesis of a [2] catenane by use of a negative templating steric barrier as an auxiliary linkage.71...

Scheme 10.21 Statistical and directed synthesis of the first hydrocarbon catenane.74...

Raymo, F.M., Stoddart, J.F. Organic Template Directed Synthesis of Catenanes, Rotaxanes and Knots. In ref. 4b, p.143. 

The -electron-deficient pyridinium ring has played an important role in template-directed synthesis in which the interaction of a -electron acceptor and a -electron donor facilitate self-assembly. This has led to the construction of a variety of supramolecular assemblies including catenanes (linked rings) and rotaxanes (wheel and axle) . 

Fig. 8 The two applied approaches to catenane synthesis prior to 1983. (a) The first statistical synthesis [58] relied upon the macrocyclization of a linear compound (7) in the presence of a deuterated cycloalkane (III) to achieve small amounts of the catenane V. (b) The first example [59] of directed synthesis by covalent templation was a catenane that formed after cleaving the covalent bonds around the aromatic core in compound 16. Reproduced with permission from [58] (copyright 1960 American Chemical Society), [59] (copyright 1964 Wiley-VCH)...

Directional synthesis. In April of 1964 in the laboratory of the Freiburg University G. Schill and A. Liittringhaus succeeded in the directional synthesis of a catenane according to the following chart ... 

Often in this book we refer to selectivity as the most burning problem of organic synthesis and mentioned that complexation may be employed as an efficient tool to deal with this problem. This same principle was successfully applied to the elaboration of the directed synthesis of catenane structures. 

In 1989, following extensive preparatory work discussed, the template-directed synthesis of the positively charged [2]-catenane 5 was reported by the Stoddart group (Figure 5.2). Only mild conditions were required, with the crystalline catenane... 

Figure 5.17 The multistep template-directed synthesis of the high-order catenanes...

Metal-directed Synthesis - Rotaxanes, Catenanes, Helicates and Knots... 

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