Resorcarenes conformations

Figure 6.3 Upper- and lower-rim intramolecular hydrogen-bonding interactions in calix[4] arenes and [4] resorcarenes, which stabilise the cone conformations.

Atwood et al. have gone on to prepare a truly enormous molecular capsule along these principles, which conforms to the geometry of a snub cube (structure (1) in Figure 10.47). Reaction of six equivalents of the octol [4] resorcarene (with either methyl or undecyl feet ) with eight water molecules results in... 

It seems appropriate at the outset to review some basic features of calixarenes and resorcarenes. Four basic conformations have been discussed for calix[4]arenes... 

There are other examples in which the directionality of hydrogen bonds follows more stringently from the NMR spectra. Aminomethylation of resorcarenes leads to 118, which was found in a C4-symmetrical conformation in the crystalline state. 

Calixarenes are macrocyclic molecules synthesized with high yield by condensation of appropriate arenes and aldehyde derivatives. Calix means bowF in Latin and Greek, and this phrase reflects the shape of the tetramer, which usually adopts a bowl or beaker-like conformation. Gutsche first introduced the name calixarene for this class of compounds [38]. Several authors have exhaustively reviewed the chemistry and synthetic procedures, which lead to different structural modifications of calixarenes [39-42]. In general, three types of calixarenes derivatives are known first, metacyclophanes (type 1) second, those obtained by condensation of formaldehyde with phenol (type 11), and third, those obtained by reaction with resorcinol (type III) (Scheme 6). The latter modifications are also called resorcarenes to distinguish calixarenes of type III from those of type II. 

The preferred conformation of resorcarenes is different for the various diastereomers. The rccc isomer assumes a cone crown) conformation with an axial orientation of the residues R, which can be distorted to a so-called boat conformation where two opposite rings are more or less parallel, while the remaining two are bent away from the cavity becoming nearly coplanar. The cone conformation with an all-equatorial orientation of R was never observed. The rctt isomer is always found in a chair conformation, in which... 

The conformational instability of DPM is partially transmitted to derivatives that are important in supramo-lecular chemistry, such as cavitands. " " Resorcarenes are conformationally mobile, with a AG for the rotation... 

Calixarenes, for example, 2.120, have already been discussed as hosts for cations and both cation and neutral molecules simultaneously in Sections 2.3.6 and 2.5.5, respectively. Resorcarenes e.g. 2.121) are very closely related to calixarenes and are sometimes referred to as calixresorcarenes. They are prepared from the acid-catalysed condensation of resorcinol (1,3-dihydroxybenzene) with aldehydes, a reaction first carried out by Baeyer in 1872. This macrocycle is arguably one of the most important molecules in the field, as resorcarenes serve as the basic building blocks for many cavitands and (hemi)carcerands. Both calixarenes and resorcarenes posses a shallow bowl-shaped conformation in their most stable forms. However, [4]resorcarenes (the [4] prefix refers to the ntimber of resorcinol units that make up the molecule, just as in calix[n]arenes) tend to produce a... 

Treatment of tetraalcohol 25b with glutaroyl, adipoyl and pimeloyl dichlorides in the presence of Et3N gave the corresponding double-spanned resorcarenes 26 (n=l), 27 (n = 2), and 28 ( = 3) [15], in which the insertion of the methylene bridges led to the formation of a cavity shaped architecture resembling a basket (Scheme 8.8) H- and C-NMR spectra. X-ray analysis, as well as molecular dynamic studies agreed that the basket derivative had a frozen flattened-cone conformation. 

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