Bridged calixarenes

By bridging calixarenes 226 [9], forming their dimers like 227 with one or several bridges [10] or by combining them with crown ethers 228[11], calixarenes with several novel architectures and complexation behaviour have been obtained. Some of such systems have been proposed as prospective sensors. 

A potential oxidability to sulfoxide and sulfone for providing new sulfur-bridged calixarenes... 

Two calix[4](diseleno)crown ethers were synthesized by the treatment of the disodium salt of 1,3-propanediselanol with preorganized 1,3-dibromoethoxycalixarenes the 1,3-Se-bridged calixarene forms an infinite sheet aggregate by means of self-inclusion and intermolecular Se—Se interactions in the solid state <02TL131>. 

The preorganization of the receptor molecule by introduction of an ethyleneoxy bridge imit at the upper rim was also described [131]. The cavities of these bridged calixarenes (27) were larger than the lower rim bridged calixarenes and extraction experiments were done with both solid alkali metal and ammonium picrates into chloroform. The measurements showed that these calixarenes have a lower affinity for alkali metal ions (extraction <3%) than the lower rim bridged calix[4]arenes. However, primary ammonium ions were efficiently extracted with efficiencies of 27-57%,... 

The prototype of the lower rim A,C ring-bridged calixarene is the calix-... 

By turning the bimacrocycle upside-down, onr concave concept was termed some years later as reaction bowls. Functional groups including less stable ones such as a sulfenic acid, a selenenic acid, and a monosubstituted simple enol have been incorporated in cyclophanes and bridged calixarenes (for an example see Fignre 7.15). 

Figure 7.17 Concave 1,10-phenanthrolines can also be obtained in one-step or two-step macrocyclizations starting from appropriately 2,9-disubstituted 1,10-phemmthrolines. Here the TL conformer (X, Y = polyethylene glycol orY = polymethylene) of a two step macrocyclization starting from a 1,10-phenanthroline containing monomacrocycle is shown. For a one-step macrocyclization see Figure 7.10, and for a bridged calixarene see Figure 7.15...

In contrast in the bridged calixarene (see Figure 7.15), the methyleneoxy units between the 1,10-phenanthroline and the calixarene act as flexible joints and this leads to a different geometry in which the 1,10-phenanthroline bridge is tilted towards one chain of the calixarene rim. The calixarene macrocycle is too small to accommodate the carboxylate or to let an alkene approach the carbenoid. This results in an orientation in which both, the alkene and the carboxylate residue of the carbene moiety, have to be squeezed in the gap between the 1,10-phenanthroline and part of calixarene rim. By this sterical shielding of the calixarene, the carboxylate and the residues of the alkene are oriented next to each other, and thus the predominant formation of the endo-product is observed. " ... 

K. -L Koike. M. Preparation and conformational studies of ethylene-bridge calixarene-analogous macrocyclic meta-cyclophanes. Chem. Ber. 1993. 126. 2501. 

Brindley, G.D. Fox. O.D. Beer, P.D. Ferrocene-appended and bridged calixarene ligands for the electrochemical sensing of trivalent lanthanide ions. J. Chern. Soc., Dalton Trans. 2000, 4354-4359. 

Another way of fixing the cone conformation has been achieved recently by the connection of two opposite para-positions by an aliphatic chain of appropriate length producing a bridged calixarene (135) (135) (Figure 2.58). 

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