Catenanes statistical methods

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. 

This threading and stoppering technique was used by Schill and coworkers for a very elegant synthesis of a hydrocarbon catenane [54, 55]. The intermediate rotaxane was prepared in gram scale amounts, exemplilying the preparative value of the statistical method. 

The first catenanes and rotaxanes were constructed by either statistical [2] or directed [3] synthetic approaches. The statistical method relies [2] on the formation of small quantities of a species in which a cyclic molecule is threaded by an acyclic molecule. After experiencing appropriate covalent bond formation, these threaded species are con-... 

The statistical method of syntl s of topological compounds can be divided into a truly statistical synthesis and a thesis with elements of directionality. Prq>aring catenanes by the statistical method is described in ddail by Sdiill in his monograph The statistical technique of synthesis of rotaxanes will be presented here in greater detail. The scheme of the technique is as follows bulky end groups are connected to a linear molecule in the presence of a macrocycle. Sudi a re kn, where the macrocycle remains imchanged, results in the formation of some amount of rotaxane and a molecular dumb-beU ... 

These data indicated that the acyloin, cycle is intertwined with C34He3D. Initially Wasserman recovered 5.66 mg of catenane oil, the total yield being 0.0001 per cent. Subsequently Wasserman and coworkers developed other methods of statistical synthesis of catenanes. 

The breakthrough in catenane synthesis occurred when the statistical and covalent template methods were abandoned in favor of approaches that relied... 

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