Introduction of Glyco, Peptido, Carboxy, and Alkyno Substituents at the Calixarene Exo Rim via the p-Bromodienone Route

Direct meta substitution of calix[4]arenes

Calixarenes represent very popular building blocks in supramolecular chemistry. Compared to other macrocyclic families, they exhibit an almost infinite possibility of derivatization of the basic skeleton, which makes them ideal candidates for the design of new receptors or other functional systems. Although the chemistry of calixarenes is well established, there are still some substitution patterns that are unavailable or require a very lengthy synthetic approach. Among such synthetic challenges is the meta substitution of the aromatic skeleton (relative to phenolic oxygen), which, in conjunction with the 3D structure of calixarenes, leads to the inherent chirality and enables the synthesis of derivatives with a hitherto undescribed topology. This review deals with the current achievements in the meta substitution of calixarenes.

Facile synthesis of a C4-symmetrical inherently chiral calix[4]arene

Inherently chiral calix[4]arenes with C₄-symmetry are extremely rare and difficult to synthesise, severely hampering any effort to expand on their potential as chiral supramolecular catalysts and building blocks. Herein we report a reaction of a tetracarbamate calix[4]arene with NBS which results in a high yield of an inherently chiral calix[4]arenes with C₄-symmetry. Furthermore, employing a chiral N-Boc proline moiety allows for separation of the diastereomers formed, thus obtaining the pure enantiomers after hydrolysis. The enantiomers could be assigned based on the CD spectra and DFT calculated values.

Regio- and stereoselectivity of spirodienone formation in 2,14-dithiacalix[4]arene

Within the mixed-bridge system the thiacalixarene fragment (Ar–S–Ar) is much more prone to spirocyclization than the calixarene one (Ar–CH₂–Ar).

Regioselective SNAr reaction of the phenoxathiin-based thiacalixarene as a route to a novel macrocyclic skeleton

The formation of a novel type of macrocyclic skeleton possessing meta- and para-bridging units can be achieved by S_NAr cleavage of an easily accessible phenoxathiin-based thiacalix[4]arene.

Chemoselective oxidation of phenoxathiin-based thiacalix[4]arene and the stereoselective alkylation of products

Phenoxathiin-based thiacalix[4]arene was subjected to exhaustive oxidation. Depending on the reaction conditions, the macrocyclic systems bearing four sulfonyl groups or three sulfonyl and one sulfoxide group are available in high yields.

Nucleophilic Functionalization of the Calix[6]arene Para- and Meta-Position via p-Bromodienone Route

It is here demonstrated that the p-bromodienone route, previously reported for calix[4]arenes, is also effective for the functionalization of the calix[6]arene macrocycle. Thus, alcoholic O-nucleophiles can be introduced at the calix[6]arene exo rim. In addition, the reaction of a calix[6]arene p-bromodienone derivative with an actived aromatic substrate, such as resorcinol, led to the first example of a meta-functionalized, inherently chiral calix[6]arene derivative.

Application of RDC enhanced NMR spectroscopy in structural analysis of thiacalix[4]arene derivatives

The conformational behaviour of novel phenoxathiin-based skeletons was studied using the Residual Dipolar Coupling constant (RDC) method.

Use of residual dipolar couplings in conformational analysis of meta-disubstituted calix[4]arenes

Dimercuration of tetrapropoxy calix[4]arene followed by a reaction with isoamyl nitrite afforded dinitroso regioisomers with unique substitution patterns. The unusual conformational behaviour of these inherently chiral systems was revealed by the combination of dynamic NMR and residual dipolar coupling (RDC) techniques.