Cyclophanes carcerands

It should be stressed that calixarenes, hemispherands and spherands, carcerands and hemicarcerands, and some other molecules discussed elsewhere in this book, belong to the cyclophane group of compounds. 

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). 

Calixarenes, cavitands, carcerands, and cyclophanes as nanoscale molecular containers 02BCJ393. 

The preceding molecular baskets belong broadly to two classic classes of macrocycles namely the calixarenes and cycloveratrylenes. There are several other macrocycles with the potential to bind guests in an aromatic-rich cavity that are worthy of discussion. Of the vast amount of work that emanated from the Cram group, the rigid spherands and carcerands stand out. In addition there are the cyclophanes and Baeyer s early contribution to macrocyclic chemistry, resorcinar-enes and calixpyrroles. 

A different use of inclusion was realized with carceplexes [7] starting from concave cyclophanes, such as cavitands, carcerands with an inner sphere were synthesized or non-covalently assembled [ 8]. Reactive molecules, trapped in the interior and so shielded from reaction partners could be investigated by spectroscopy. Cyclobutadiene [9] and benzyne [10] are the most striking examples of highly reactive molecules isolated by this technique. 

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.

Host inolecules may be broadly classified into two main types those that form molecular complexes by fitting convex guests into the concave cavity of the host (examples include cyclodextrins, cyclophanes. calixar-enes, cycloveratrylenes, and various carcerands ) and those that form lattice inclusion compounds by packing in such a manner as to leave cavities, channels, or layers in the crystal structure so as to accommodate various guest... 

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. 

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