Tetrameric calix arenes

As in the case of the tetrameric macrocycles discussed above, compounds 17 and 18 can be considered as porphyrinogen analogues or as heteroatom-bridged heteroaromatic calix[4]arene derivatives. The two different conformations observed for 17 and 18 have analogues in compounds 16 (Fig, 5) [15, 28-30],... 

Much interest has centred on the branch of cyclophanes known as calixarenes. They are polyphenol systems that can act as hosts in the formation of inclusion compounds, where a small guest molecule resides completely in a cavity within a single host they are cone-shaped cavitands . Several accounts have appeared of their history. The discovery by Baeyer of a formaldehyde/phenol resin led to Bakelite and to the work of A. Zincke and E. Ziegler, who gave to the first oligomer a tetrameric structure of a calix[4]arene. Later syntheses by Gutsche (1978) led to calixarenes with 4, 6 or 8 phenol residues.107-109... 

Naphthol may form cyclic tetrameric condensation products with formaldehyde among which 101 has a C4 axis.194 However, since the OH groups are in exo positions in this case (in contrast to the calix[4]arene 97g derived from 2-naphthol) it seems difficult to fix a nonplanar conformation in these cases.195 A possibility would be the connection of two opposite oxygens by a (crown) ether bridge which would lead to a C2-symmetrical derivative. 

Tetrameric caHx[2]benzimidazolone[2]arenes 178a and 178b and octameric calix[4]benzimidazolone[4] arenes 179a-f, have been formed by high dilution and template induced condensation of l,3- > (bromomethyl)benzene and the trinuclear... 

When we reinvestigated the base-induced reaction of 1-naphthol with formaldehyde we isolated and identified three isomeric tetrameric compounds [2] which we named calix[4]naphthalenes by analogy with the calix[4]arenes and cal-ix[4]resorcinarenes. However, unlike the latter which are derived fromp-substituted phenols and resorcinol respectively, several different isomers can theoretically exist for the calix[4]naphthalenes. Additionally, the conformations that are possible for some of these isomers are further complicated due to the dissymmetry that is introduced by the naphthalene rings. In this contribution we will describe some properties of this new class of compounds. 

The calix[4]arene-based ligand syntones 129-133 with either aryl urea or sulfonylurea fragments on the upper rims in their cone-conformation gave small hydrogen-bonded capsules 338-342 by Scheme 3.24, while their heterodimeric capsules have been exclusively formed when both aryl- and sulfonylureas-containing syntones are present in solution [25]. All these homo- and het-erodi- and tetrameric capsules are able to reversibly encapsulate suitable guests in organic media. 

Calix[4]resorcinarenes 76 are tetrameric cavity compounds produced by the reaction of an aldehyde and resorcinol (Figure 50.24). Calixarenes 77 are produced by the reaction of phenol and formaldehyde. Chirality in calixarenes and calix[4]resorcinarenes is usually achieved by the addition of enantiomeric ally pure moieties. Although several calLx-arenes and calix[4]resorcinarenes have been examined as chiral NMR shift reagents, only one particular family of water-soluble calix[4]resorcinarenes 78-82 has been widely studied. " ... 

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