Amide-linked rotaxane

Figure 32. Porphyrin blocking groups offer the possibility of further supramolecular deri-vatization. Amide-linked rotaxane with porphyrin blocking groups 85, its Zn complex 86, and an unsymmetrically capped rotaxane 87.

Nonionic template synthesis of amide-linked catenanes and rotaxanes with macroheterocyclic fragments 97AG(E)930. 

R. Jager, F. Vogtle, A New Synthetic Strategy towards Molecules with Mechanical Bonds Nonionic Template Synthesis of Amide-Linked Catenanes and Rotaxanes , Angew. Chem Int. Ed. Engl. 1997,36,930-944. 

After the synthesis of the first amide-linked [2]rotaxanes, Vogtle et al. set out to study the limits of molecular recognition, which in terms of Emil Fischer means to discover if the lock (macrocycle) is specific to a certain key, or if several keys (monoamide threads) fit. It turned out that - in contrast to catenane formation - rotaxane synthesis is very tolerant towards the variation of the building... 

Figure 26. Synthesis of the first amide-linked [3]rotaxane 64 by Vogtle et al.

Figure 27. Syntheses of symmetrical 67 and unsymmetrical 66 amide-linked [3]rotaxanes.

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. 

Rotaxane 80e can even be dimerized by reaction with l,3,5-tris(4-methyl-phenyl)benzene (105) [42]. Considering the steric crowding, it is remarkable that the resulting wheel-tris[2]rotaxane ([4]rotaxane) 106 is formed in 35% yield (Figure 42). Extension of the strategy of coupling rotaxanes to multifunctional units should enable easy access to amide-linked dendritic rotaxane structures. 

Finally catenane 79 and rotaxane 80e were covalently bound to form the first amide-linked catrotane 108 (Figure 44) [41]. 

Amide-linked catenanes and rotaxanes can play a major role in the study of rare forms of chirality, e.g. topological chirality and cycloenantiomerism [60]. Resolution of enantiomeric catenanes, rotaxanes, and pretzelanes has been achieved by HPLC on chiral column materials, but further work must be performed to determine absolute configurations and to realize new chiral skeletons composed of achiral building blocks. Topological asymmetric synthesis still belongs to dreams of the future yet should be kept in mind. 

Jager. R. Vogtle, F. A new synthetic strategy towards molecules with mechanical bonds Nonionic template synthesis of amide-linked catenanes and rotaxanes. 26. Angew. Chem. Int. Ed. 1997, 36, 930. 

Rotaxane 80m and its intramolecularly linked derivative [l]rotaxane 100 are the first examples of rotaxane cycloenantiomers [4a]. The mirror images of 80m differ in the succession of amide and sulfonamide units with regard to the unsym-metrical axle (Figure 49). 

---