Template reactions/synthesis catenanes

Amide-linked catenanes and rotaxanes, readily accessible via nonionic template synthesis, are molecules with fascinating topology, but their final breakthrough was only achieved when they became substrates for further chemical derivatiza-tion. A potential reaction site in the catenanes and rotaxanes presented so far is the sulfonamide group, because the proton can be selectively abstracted in the presence of carbon amide groups. Subsequent alkylation offers numerous possibilities of catenane and rotaxane chemistry. 

The synthesis of interlocked molecules has become commonplace over the past 25 years with the gradual development of a number of highly facile template methods for their construction. What were once laboratory curiosities have now taken a prominent place in the broad field of supramolecular chemistry, especially regarding their uses and further potential as molecular switches and machines [1], We present here an overview of the main synthetic approaches to these molecules, with a focus on methods in which macrocyclization reactions result in interlocked products. The analysis is by no means meant to be comprehensive or exhaustive in detail, but rather to convey the variety and utility of the selected synthetic strategies in generating abiotic rotaxane and catenane superstructures. 

In this context, it should be mentioned that free cations in suitable solvents can be used as templates for the synthesis of macro(poly)cyclic compounds e.g. catenanes). Such template-based syntheses are mediated by slightly solvated metal cations, which assemble the reaction partners as ligands, allowing them to easily react with each other the desired product is obtained after removal of the template for a review, see reference [845]. 

Figure 6 shows the synthesis, templated by donor-acceptor and hydrogenbonding interactions, of [2]catenane 8 + [23]. Reaction of the dication with the... 

Scheme 3. Template synthesis by Vogtie and co-workers of amide-based catenanes with a concave template The catenation of the macromonocycle 15 with 13a and 14 leads to formation of catenane 17. The guest diacid dichloride 13a and the host 15 are locked in an orthogonal arrangement 16. The functional groups are fixed and thus preorganized for reaction with the diamine 14.

In the case of catenanes, the most rationale synthetic strategy is the clipping of a macrocycle onto a preformed one (Fig. 8). A double-clipping procedure can also be used [46]. Figure 9 shows the synthesis of a catenane templated by electron donor/acceptor interactions [45]. Reaction of a... 

Scheme 8 Reaction scheme for the chloride-templated synthesis of catenane 23...

Abstract The approach based on the copper(I)-templated synthesis of porphyrin catenanes and rotaxanes developed by the authors group is here reviewed. Zn(II) porphyrins and gold(III) porphyrins were chosen as electron donors and electron acceptors, respectively, to constitute the electro- and photoactive parts of the present systems. The processes—energy and electron transfer reactions—occiuring in the interlocked structures upon light absorption in the presence or absence of Cu(I) are presented, their rates and efficiencies critically compared and discussed with respect to properties of the components and of the ensemble. A detailed examination of differences and analogies in photoreactivity between the present and closely related systems reported by others is presented. 

An intriguing series of electro- and photoactive porphyrin catenanes and rotaxanes, obtained by the authors through copper(I)-templated synthesis, is reviewed in the sixth chapter by Lucia Flamigni, Valerie Heitz, and Jean-Pierre Sauvage. The photo-induced processes - energy and electron transfer reactions - occurring in the interlocked structures upon light absorption are discussed in detail and critically compared to closely related systems reported by others. 

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