Ring formation calixarenes

Shinkai and coworkers have capitalized on this conformation flexibility in their designs of several pyrene-derivatized calixarene chemosensors. The rotated phenyl ring of the partial cone conformer of 37 allows two pyrene units to more easily interact by decreasing steric hindrance at the lower rim [376], Addition of Li+, Na+, and K+ ions enforces cone formation and the disruption of the initially formed excimer. Accordingly, the metal ions are detected by a decrease in pyrene excimer emission and concomitant increase in the pyrene fluorescence. 

Noteworthy also is the reaction between L42 and Cul in the presence of KI. The crystal structure determination reveals the formation of hitherto unknown exocyclic Cu g2- clusters, which are linked by L42 to generate a polymeric ID array of composition pC2(Cu4I6)L42]n 42". Within the crown ether cavities of L42, two potassium ions are trapped in an endocyclic manner. Also, upon inclusion of the K+ ions the crown ring shrinks leading to opening of opposite aromatic rings in the host calixarene unit, a rare behavior for this class of compound.162... 

Clean monolithiation under equilibrating conditions means that the bromine atoms of 1,3,5-tribromobenzene may be replaced sequentially, one at a time.72 More spectacularly, it is possible to use the selective formation of the most stable lithiated species to form almost any regioisomer of a substituted calixarene.73 Tetrabrominated 68 may be monolithiated or tetralithiated, giving 69 and 71. With two equivalents of BuLi, dilithiation takes place selectively on the alternate rings of the calixarene (73), from which the diacid 74 may be formed, or after protonation the monoacids 76 or 77. The use of rc-BuLi is advantageous where precise numbers of equivalents are required, since neither elimination nor substitution of BuBr happens at low temperature butylation can be a problem on warming, however. 

The tube-like receptor 39 was shown to bind two imidazolidin-2-one molecules inside the calixarene subunits or, more interestingly, ion triplets comprising an anion, which binds to the central urea moieties, and two ammonium ions, which are incorporated into the calixarene rings [86]. Particularly stable complexes are formed with ammonium sulfate salts even in relative polar media (CD3OD/ CDCI3 3 1), but chloride ions can also induce the formation of such complexes... 

A potential for large ring and cavity formation extends to many P-containing organic molecules, in addition to the inorganic phosphates discussed above. These compounds include phosphate derivatives of fashionable structures such as crown ethers, calixarenes, carceplexes, catenanes, rotaxanes, self-assembly molecules and so on, and varieties which are discussed in Chapter 10, such as cyclo-dextrins, phosphosaccharides, phosphoproteins and nucleic acids. Phosphorus analogues of cyclo-polypyridyls and porphyrins are discussed in Chapters 7 and 8. 

Water-soluble calix[n]arenes 20-24 with sulfonated fragments 4-6 aromatic rings) and aminomethylated calix[4]arenes were used as components in the catalytic system for the cross-coupling reactions of l-iodo-4-phenylbenzene and phenylboronic acid (Suzuki reaction) catalyzed by palladium complexes with sulfonated triphenylphosphine (Scheme 4.13) [65], Addition of water-soluble calixarenes increased the yield of reaction products more than twofold. The maximum activity was exhibited by calixarenes containing amino groups 22-24. The appropriate constants of the formation of respective inclusion complexes were significantly higher. 

Resorcinol and pyrogallol are benzene derivatives that have two and three hydroxyl groups, respectively. They react readily with aldehydes to form macrocycles that are similar in some aspects to the calixarenes [16]. The formation of calixarenes involves reaction of phenol at the 2,6-carbons, through which the methylene link forms. Resorcinol is 1,3-dihydroxybenzene, and as with pyrogallol, 1,2,3-trihydroxybenzene, the ring-forming links occur at the 4- and 6-positions. Exemplary structures are shown in Fig. 8.3. 

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