Catenane synthesis

In 1995 Leigh et al. reported a catenane synthesis that is convincing not only because of its simplicity but also because it is accessible to a wide variety of reactants [24]. When isophthaloyl dichloride (3) was reacted with l,4-bis(aminometh-yl)benzene at high dilution [2]catenane 28 was isolated in 20% yield without further purification by column chromatography (Figure 13). 

Figure 13. Catenane synthesis according to Leigh et al. simple and variable at the same time.

While the above mentioned clipping method with larger wheels than the rather narrow 51 was not successful, die amide systems that had been developed by Vogtle et al. for catenane synthesis seemed ideal for submission to the threading... 

The synthesis of polycatenanes requires, like the synthesis of catenanes, the preorientation of the macrocycle precursors into a favorable geometry before cycliza-tion (Scheme 4) [5], This pre-orientation is commonly achieved via a template, resulting from rc-donor-acceptor interactions, hydrogen-bonding, and coordination bonds [1-3, 5, 41], The use of a template in catenane synthesis is the subject of Chapters 4 and 6-8 and will not be treated further in this section. The aim of this section is to present the state of the art of the various synthetic approaches leading to the polycatenane polymers and networks. 

Scheme 2 A catenane synthesis based on it -donor/h-acceptor interactions. Instead, the...

One question of course was, what the scope and limitations of the new catenane synthesis were and how the yields of the catenane could be increased. The first step towards greater variability of this synthesis was the stepwise sequence shown in Scheme 8. It permits the generation of macrocycles which are desymmetrized with respect to their two dicarboxylic amide building blocks. Many catenanes with such wheels can be synthesized by this strategy.26 It turned out that the product... 

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 10.11 The first catenane synthesis via the statistical approach.57...

Although structurally and functionally appealing, the synthetic ways to build these species remained a hard task until mid 80s. Then, a strategy was developed by Sauvage and his co-workers that used coordination to a Cu(I) ion prior to the macrocyclization in the catenane synthesis (Figure la). The metal that served as a template with tetrahedral coordination geometry was then removed by demetallation with cyanide [8],... 

Fortunately, more efficient methods for the complexation of macrocyclic hosts with acyclic guest molecules have become available with the advent of supramo-lecular chemistry, resulting in higher yields in rotaxane and catenane synthesis. In the following sections, the preparation of different types of interlocked molecules, with the use of host-guest recognition, is discussed. It should be noted that these template-directed methods differ significantly from the above-mentioned stochastic approach [28]. 

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