Catenanes isomers

Scheme 14. Catenane isomers 40-42. The rings bearing the substituents OUT (IN) of the catenane structure are referred to as OUT (IN) rings, respectively.

Singly and doubly interlocked [2]-catenanes isomer(see p. 163 for a discussion of diastereomers). Catenanes 37 and 38 are such stereoisomers, and would be expected to have identical mass spectra. Analysis showed that 37 is more constrained and cannot readily accommodate an excess of energy during the mass spectrometry ionization process and, hence, breaks more easily. 

Figure 5.8 A single enchainment stereo isomer is obtained in the acetylcholine templated synthesis of a [2] catenane.

The two possible coconformational isomers of such catenanes can be interchanged by appropriate stimuli. In a diagram of potential energy against rotation angle of the asymmetric macrocycle, the two coconformations correspond to energy minima, provided by the intercomponent noncovalent bonding interactions. The... 

Figure 13.21 The two coconformational isomers associated with a catenane incorporating two different recognition sites within one of its two macrocyclic components can be interchanged by appropriate stimuli (S, and S2).

In the major isomer, the bipyridinium unit is located inside the cavity of the macrocyclic poly ether and the /7Y//7,v-bis(pyridinium)ethylene unit is positioned alongside, as confirmed by the electrochemical analysis. The cyclic voltammo-gram of the catenane shows four monoelectronic processes that, by a comparison with the data obtained for the free cyclophane, can be attributed as follows the first and third processes to the first and second reductions of the bipyridinium unit, and the second and fourth ones to the first and second reductions of the trans-bis (pyridinium)ethylene unit. The comparison with the tetracationic cyclophane also evidences that all these reductions are shifted toward more negative potential values (Fig. 13.33b). 

Figure 17. The degenerate forms A and B of the [2]catenanes 32-4PF6-38-4PF6 and the translational isomers A and B of the [2]catenanes 394PF6-48-4PF6.

Two-dimensional NMR studies and mass spectrometry identified the isomers as being the cyclic tetramer 6 and the [2]catenane 7 consisting of two interlocked cyclic dimers. Later X-ray crystal structures confirmed these results [16, 17],... 

A) the in/out isomer 14 and the out/out isomer 15 were obtained, depending on which of the two possible niches of the first formed macrocycle is used for the intercalation of the monoamide. The third possible (in/in) isomer 16 could finally be formed when the substitution pattern was reversed (pathway B). The two pathways differ in the embedding compound, and interestingly for route B, where the nesting component bears the substituent, significant steric hindrance seems to accompany catenane formation - catenane 14 was obtained in only 2.7% yield, whereas route A leads to 17% of the same catenane. 

In contrast, when the substitution pattern is reversed, i.e. the 2,5-fiirane unit is incorporated in the diamine moiety 25 and reacted with isophthaloyl dichloride (3), not only macrocycle 24, but also the two possible isomeric catenanes 26 and 27 are formed. This suggests that the isophthaloyl unit is a better guest or reacts quicker than the furanoyl moiety. The yields obtained for 26 (20%) and 27 (8%) indicate that the isophthaloyl-guest in the second macrocyclization prefers the west-side a) niche of the host 24. Both isomers, the in/out 26 and the out/out 27 furano catenane could be crystallized and their X-ray crystal structures were... 

When macrocycle 65 is synthesized, the in/out isomer of [2]catenane 79 is also formed in 11% yield (Figure 29) [46]. A first attempt to methylate both sulfonamide groups by treatment of the DMF solution of 79 with iodomethane and potassium carbonate was successful. By bridging the two sulfonamide units with a bifunctional alkylating reagent, we were able to synthesize the first pretzel-shaped molecule [54]. Considerations of the X-ray structure analysis of amide-linked catenanes [16] and CPK models led to the diiodo compound 95 as a suitable brid-... 

It has been observed that the isomers 41c,d and 42c,d have the same low reactivity towards polycondensation, irrespective of the reaction conditions and that only oligo[2]catenanes were reached [30, 56], This important finding rules out the... 

Scheme 21. Synthesis of the poly[2]catenane 59. For the sake of clarity, the counter-ions have been omitted and only one isomer is represented [62].

Scheme 9 Chemically and electrochemically driven translational isomer switching of [2] catenane 17 [56]...

The synthesis of bis[2]catenanes outlined in Scheme 5.15 allows not only the preparation of compounds with identical loops (12a). The rings attached to the second bisloop calix[4]arene may be also different from those of the first calix[4]arene (12b) [55]. Two regioisomeric bis[2]catenanes are possible, where the two rings attached to a given calix[4]arene are different (Figure 5.12) The isomer 12c can be selectively synthesized from a bisalkenyl urea, where the other two urea functions are connected to a loop, while the third regioisomer 12d would be not so easily available. 

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