Cryptophanes cyclophanes

The spherically shaped cryptophanes are of much interest in particular for their ability to bind derivatives of methane, achieving for instance chiral discrimination of CHFClBr they allow the study of recognition between neutral receptors and substrates, namely the effect of molecular shape and volume complementarity on selectivity [4.39]. The efficient protection of included molecules by the carcerands [4.40] makes possible the generation of highly reactive species such as cyclobutadiene [4.41a] or orthoquinones [4.41b] inside the cavity. Numerous container molecules [A.38] capable of including a variety of guests have been described. A few representative examples of these various types of compounds are shown in structures 59 (cyclophane) 60 (cubic azacyclophane [4.34]), 61a, 61b ([4]- and [6]-calixa-renes), 62 (cavitand), 63 (cryptophane), 64 (carcerand). 

Loops correspond to compounds like ansa cyclophanes, but equally well they might induce the design of novel annelated benzenes. Simple and polycycles manifest the familiar classes of cyclophanes and cryptophanes commonly synthesized by practitioners of supramolecular chemistry [12,13]. The Platonic graphs are a subset of the polycyclic, but, because of their potential for high symmetry and structural simplicity, they form an especially provocative group. 

A further example of a tailor-made host compound is cryptophane (162) By use of this cyclophane derived from the triveratrylene skeleton and having a large cavity inside the molecule, the differentiation of bromochlorofluoromethane (136) was successfully carried out on an analytical scale. Bromochlorofluoromethane has also been optically enriched through complexation with brucine... 

Carcerands and Hemicarcerands, p. 189 Concave Reagents, p. i /1 Crown Ethers, p. 326 Cryptophanes, p. 340 Cyclodextrins, p. 398 Cyclodextrins, Applications, p. 405 Cyclophanes Definition and Scope, p. 414 Enzyme Mimics, p. 546 Macrocycle Synthesis, p. 830 Organometallic Anion Receptors, p. 1006 Soft and Smart Materials, p. 1302 X-Ray Crystallography, p. 1586... 

Fig. 4 Exemplary cases of enforced cavity hosts and their supramolecular compounds (guests symbolized in broken rings) (a) Cleft-type (b) tweezer-type (c) spherand (d) cyclophane (monocyclic) (e) cyclophane ibicyclic) (f) cavitand (g) carcerand (h) calixarene (calix[4]arene) (i) resorcarene (j) cryptophane (k) cyclodextrin (P-cyclodextrin) and (1) cucurbituril.

The C3 symmetry of the cup-lilie trimers indicates that they are chiral typically being formed as a racemate. In some cases, the cups are resolvable via suitable dia-stereomers. as the enantiomers are somewhat stable to racemization via conformational inversion of the nine-membered cyclophane ring (AG 298 = 110-1 i5 kJ/mol). Chirality in the cup-shaped units implies that two types of cryptophanes exist Joining two cups of opposite... 

Over the last 10 years or so, numerous books (Dieder-ich and Vogtle are particularly recommended) and chapters in books were published, covering many aspects of cyclophane chemistry. Readers are pointed to a recent review on " Synthetic Receptors that also embraces many aspects of cyclophane chemistry. It is the intention of this article in the Encyclopedia to focus on more recent developments toward the end of the last century and the turn of the new millennium. The examples chosen are in no way exhaustive but rather serve as pertinent examples to emphasize the types of cavities the cyclophane receptors possess and interactions that drive complexation. Where possible, the bioinimetic nature of the receptors will be discussed because the ultimate goal in much of cyclophane work is to mimic nature s processes. It is hoped that the reader will see the cross-fertilization of cyclophane chemistry and how examples discussed in other articles on. for example, cyclodextrins, cryptophanes. cavitands, crown ethers, etc., are just as relevant to this article. 

Inclusion complexation has developed to becoming another widely exploited supramolecular interaction for the formation of supramolecular polymer networks, mostly in water [197, 198]. Several classes of macrocycles have been developed, including crown ethers [199, 200], porphyrins [201, 202], cyclophanes [203], catenanes [204], cavitands [205, 206], cryptophanes [207], calix[n]arenes [208], and carcerands [209]. Macrocyclic-based supramolecular gels can either be formed from low molecular weight precursors or from macromolecular building blocks. The following discussion focuses on the latter. 

Cryptophane A host that combines the structural features of a cryptand and a cyclophane. Typically two cone-shaped cyclotriveratrylenes are linked with three bridges to create an enforced cavity. 

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