Enantiomers, amide rotaxane

Fig. 4 Two enantiomers of an amide rotaxane. showing their overall structures. Note that the sulfonamide group in the wheel defines an atom sequence (indicated by the arrows in the bottom drawings). The sulfonamide incorporated in the axle permits the two stoppers to be distinguished. Such rotaxanes can be separated into the two enantiomers by HPLC on chiral stationary phases, and their CD spectra were measured.

Undoubtedly, the most important stereochemical feature is chirality. The [2]-rotaxane depicted schematically in Figure 2.12a is made with a macrocycle and a dumbbell that are not themselves chiral but oriented by appropriate substitution patterns on these components. Vogtle and co-workers described cycloenantiomeric rotaxanes that are based on the amide templating functionality (Figure 2.13).36 Racemic [2]-rotaxane 34 was synthesized in 20% yield by reaction of unsymmetrical acid dichloride 32 with trityl aniline 33 in the presence of macrocycle 31. The object and its mirror image are created by different sequences of the amide and sulfonamide linkers in both the dumbbell and the macrocyclic component. If the order of the atoms within the dumbbell is examined, in one enantiomer the sulfonamide nitrogen atom is... 

The best yield obtained for a [2]-rotaxane was 41%, in the case of a mixed sulphonamide/amide spacer [104], Combining this non-symmetrical spacer and a raacrocycle oriented by alternating sulphonamide and amide linkages, allowed the preparation of chiral rotaxanes, which could be resolved into the separated enantiomers by HPLC on optically active stationary phases [66]. 

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