Synthesis supramolecular chemistry

Keywords Dendrimers, linear aliphatic molecules, oligophenylenes, repetitive synthesis, supramolecular chemistry. 

E. Weber, ed., Supramolecular Chemistry I - Directed Synthesis and Molecular Recognition, Sponger, Bedia-Heidelberg, 1993. 

For former reviews on parts of the topic, see Refs. [10-12]. The subject is increasingly attractive and has now far-reaching applications in organic synthesis and supramolecular chemistry. 

Cyclophanes or 7r-spherands have played a central role in the development of supramolecular chemistry forming an important class of organic host molecules for the inclusion of metal ions or organic molecules via n-n interactions. Particular examples are provided by their applications in synthesis [80], in the development of molecular sensors [81], and the development of cavities adequate for molecular reactions with possible applications in catalysis [82]. The classical organic synthesis of cyclophanes can be quite complex [83], so that the preparation of structurally related molecules via coordination or organometallic chemistry might be an interesting alternative. 

Calixarenes, which are macrocyclic compounds, are one of the best building blocks to design molecular hosts in supramolecular chemistry [158]. Synthesis of calix[4]arenes, which have been adamantylated, has been reported [105, 109]. In calix[4]arenes, adamantane or its ester/carboxylic acid derivatives were introduced as substituents (Fig. 29). The purpose of this synthesis was to learn how to employ the flexible chemistry of adamantane in order to construct different kinds of molecular hosts. The X-ray structure analysis of p-(l-adamantyl)thiacalix[4]arene [109] demonstrated that it contained four CHCI3 molecules, one of which was located inside the host molecule cavity, and the host molecule assumed the cone-like conformational shape (Fig. 30). 

Sauvage, J.-P. Dietrich-Buchecker, C. O. Chambron, J.-C. Transition metals as assembling and templating species synthesis of catenanes and molecular knots. In Comprehensive Supramolecular Chemistry, Sauvage, J.-P. Hosseini, M.W., Ed., Publisher Elsevier, Oxford, UK 1996 Vol. 2, p 43. 

In supramolecular chemistry [31] iterative synthesis is frequently used for the construction of ribbon and belt shaped molecules [32]. The repeated Diels-Alder reaction is suitable for the preparation of beltenes, collarenes and cycla-cenes containing partially or fully unsaturated annelated six-membered rings. They are potential molecular receptors for appropriate substrates. Stoddart et al. synthesized the cyclacene 18 by Diels-Alder cyclization of the bisdiene 15 and the bisdienophil 16 [33] (Fig. 10). 

The synthesis of the macrocycles 43 (Scheme 9) is an example of repetitive, highly stereoselective Diels-Alder reaction between bis-dienes 41 and bis-dienophiles 42, containing all oxo or methano bridges syn to one another. The consecutive inter- and intramolecular Diels-Alder reactions only succeed at high pressure. Obviously, both reactions are accelerated by pressure. The macrocycles are of interest in supramolecular chemistry (host-guest chemistry) because of their well-defined cavities with different sizes depending on the arene spacer-units. 

Noncovalent interactions play a special role in synthetic procedures used to assemble various types of supramolecular species. These syntheses rely on the stabilization provided by non-covalent interactions between recognition sites incorporated within precursors. Various types of non-covalent interactions can be used as a recognition motif utilized to guide the synthesis.Targeted synthesis of macro- and supramolecular structures of various sizes, shapes, and functionality has now become possible. Supramolecular chemistry offers incredible applications in various fields such as medicinal chemistry (drug delivery systems),host-guest chemistry,catalysis,and molecular electronics. ... 

Emphasis on the new objectives and targets, as well as on the role that organic synthesis should play from now on in the new areas of supramolecular chemistry and bioorganic chemistry (Chapter 1), is made. 

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