Rotaxane, organic synthesis

Topics which have formed the subjects of reviews this year include excited state chemistry within zeolites, photoredox reactions in organic synthesis, selectivity control in one-electron reduction, the photochemistry of fullerenes, photochemical P-450 oxygenation of cyclohexene with water sensitized by dihydroxy-coordinated (tetraphenylporphyrinato)antimony(V) hexafluorophosphate, bio-mimetic radical polycyclisations of isoprenoid polyalkenes initiated by photo-induced electron transfer, photoinduced electron transfer involving C o/CjoJ comparisons between the photoinduced electron transfer reactions of 50 and aromatic carbonyl compounds, recent advances in the chemistry of pyrrolidino-fullerenes, ° photoinduced electron transfer in donor-linked fullerenes," supra-molecular model systems,and within dendrimer architecture,photoinduced electron transfer reactions of homoquinones, amines, and azo compounds, photoinduced reactions of five-membered monoheterocyclic compounds of the indigo group, photochemical and polymerisation reactions in solid Qo, photo- and redox-active [2]rotaxanes and [2]catenanes, ° reactions of sulfides and sulfenic acid derivatives with 02( Ag), photoprocesses of sulfoxides and related compounds, semiconductor photocatalysts,chemical fixation and photoreduction of carbon dioxide by metal phthalocyanines, and multiporphyrins as photosynthetic models. 

Frisch, H.L. and Wasserman, E. (1961) Chemical topology, J. Am. Chem. Soc. 83, 3789-3794. Schill, G. (1971) Catenanes, rotaxanes and knots. Academic Press, New York. Walba, D.M. (1985) Topological stereochemistry. Tetrahedron 41, 3161-3212. Dietrich-Buchecker, C.O. and Sauvage, J.P. (1987) Interlocking of molecular threads From the statistical approach to the templated synthesis of catenands, Chem. Rev. 87, 795-810. Philp, D. and Stoddart, J.F. (1991) Self-assembly in organic synthesis, Synlett 445-458. 

Also, from the dendrimer point of view, the introduction of mechanical bonds to dendrimers has an enormous potential to alter the properties of dendrimers in a controlled way. For example, in the synthesis of a Type II rotaxane dendrimers, the wheel components are introduced to the terminal groups of the dendrimers. This can improve the solubility of dendrimer in organic and/or aqueous media due to the formation of complexes soluble in such solvents. 

Active template methodology. In this method, recently explored by Leigh et al. [16, 17], the rotaxane is formed via synthesis of the guest molecule in the presence of the macrocyclic host, where the guest ions or organic molecules play an active template role in promoting rotaxane formation. 

Hiibner GM, Reuter C, Seel C, Vogtle F (2000) Rotaxane synthesis via nucleophilic substitution reactions the trapping of electrophilic threads by organic anion-wheel complexes. Synthesis 1 103-108... 

Raymo, F.M., Stoddart, J.F. Organic Template Directed Synthesis of Catenanes, Rotaxanes and Knots. In ref. 4b, p.143. 

The earliest syntheses of rotaxanes were largely based on the statistical or directed methods.2,3 Statistical methods require very precise reaction conditions, and directed methods involve numerous chemicals steps. However, the use of templates allows high control of these synthetic methods resulting in efficient and precise assemblies of rotaxanes that incorporate a wide range of chemical functionalities. Two types of interactions occur in synthetic template methods (1) purely organic and (2) transition-metal-templated. In this latter case, the template can easily be removed at the end of the synthesis, whereas in the former, the interactions between the template and the components of the final rotaxane will often be maintained. Selected examples will now illustrate the statistical, the directed, and templated strategies outlined above. The transition-metal-templated route will be developed separately. 

Metallodendrimers are an interesting class of molecules in the area of dendrimer chemistry. They combine dendritic structures with the specific activity of metal complex centers. Metal coordination has facilitated the synthesis of a number of dendritic, supramolecular structures. Metals have been incorporated in all of the topologically different parts of dendrimers in the repeat or branching unit, in the molecular core and in the peripheral units. Because this field of metallodendrimers has been reviewed recently [195-197], only a few examples are given below. Other supramolecular organizations such as catenanes and rotaxanes have been mentioned previously in this chapter. 

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