Pretzelanes

Template synthesis and chirality of catenanes, rotaxanes, and pretzelanes including N-macroheterocyclic lactams and related compounds as structure components 99PAC247. 

Out of many exciting recently obtained topologically distinct structures combined rotaxanes 41,400 [23], pretzel-molecule 35 [24a] and bis(pretzelane) 401 [24b], a topologically chiral [2]catenane [25] and an interestiig catenated... 

Figure 37. Synthesis of the first pretzelane 96 by intramolecular bridging of the two sulfonamide groups bearing macrocycles of [2]catenane 79.

Sulfonamide groups incorporated in rotaxanes enable the construction of new topological assemblies provided with mechanically and covalently bonded subunits. Methylation of a [2]rotaxane containing a sulfonamide unit in the axle revealed that the substitution reaction is not sterically hindered by the macrocycle. Similar to the synthesis of the pretzelane 96, the two sulfonamide groups of rotaxane 80m were bridged with 95 to form 100 in 71% yield (Figure 39) [46]. The additional covalent bond converts the former [2]rotaxane into a [l]rotaxane and reduces the mobility of the wheel along the axle. Rotaxanes 80m and 100 are his-... 

The pretzel-shaped molecule 96 (the first pretzelane ) was synthesized by intramolecular bridging of the two sulfonamide units of 79 with a bifunctionalized podand-like chain [54]. Again the enantioseparation of 96 was accomplished with a baseline quality separation and a large separation factor (a=5.20). Preparative separation of the enantiomers enabled the detection of the circular dichrogram of 96 (Figure 48). The optical rotation values of 79 and 96 were both determined to be [aD] = 168° (Troger base [aD] = 281°). 

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. 

Figure 10.62 Cartoon and 2D molecular representation of pretzelane 10.88 and the alternative bis([2]catenane).66...

Fritz Vogtle Barcelona, Spain Rotaxanes, Catenanes. Pretzelanes- Template Synthesis and Chirality... 

Heim, C., Udelhofen, D., Vogtle, F. Amide-Based Catenanes, Rotaxanes and Pretzelanes in J.-P. Sauvage, C. Dietrich-Buchecker (eds.), Molecular Catenanes, Rotaxanes and Knots. A Journey Through the World of Molecular Topology, Wiley-VCH, 1999, pp. 177-222. 

Fig. 22 Novel MIM architectures (a) pretzelane [143], (b) macrobicyclic [4]catenane [144], (c) rotacatenane [145], (d) cyclic [2]catenane dimer [146], (e) cyclic [4]rotaxane [147], and (f) doubly threaded [2]catenane [148]...

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