Molecular baskets

Fig. 9. X-ray structure of a molecular basket containing two benzylaza crown ether fragments (compound 18). (Reproduced with permission from the Royal Netherlands Chemical Society)...

Calixarenes (23) are the macrocyclic result of condensations between phenols and formaldehyde and have been referred to as the most easily accessible molecular basket. ... 

Xu, X.X., Song, C.S., Andresen, J.M., Miller, B.G., and Scaroni, A.W. Preparation and characterization of novel C02 molecular basket adsorbents based on polymer-modified mesoporous molecular sieve MCM-41. Microporous and Mesoporous Materials, 2003, 62, 29. 

The facile condensation reaction between formaldehyde and phenols or their derivatives provides a major route into rigid macrocycles used in supramolecular chemistry. Calixarenes, the best-known class of phenol-derived macrocycles, are prepared this way, as are spherands and their relatives. Cyclotriveratrylene, however, is an excellent exemplar of the molecular basket type of ligand and has been known for the best part of a century. The basic cyclotriveratrylene synthesis is shown in Figure 3.1. The original procedure by Mrs. Gertrude Maud Robinson [1] has since been refined by others and many variations are known [2,3]. 

The preceding molecular baskets belong broadly to two classic classes of macrocycles namely the calixarenes and cycloveratrylenes. There are several other macrocycles with the potential to bind guests in an aromatic-rich cavity that are worthy of discussion. Of the vast amount of work that emanated from the Cram group, the rigid spherands and carcerands stand out. In addition there are the cyclophanes and Baeyer s early contribution to macrocyclic chemistry, resorcinar-enes and calixpyrroles. 

---