Calixarenes: From chemical curiosity to a rich source for molecular receptors

Calixarenes, the macrocyclic compounds derived from the condensation of p-substituted phenols and formaldehyde under basic conditions, have been widely used in the last ten years in Supramolecular Chemistry. Their huge success is due to several factors. They are readily accessible in large quantities, can be easily functionalized both at the phenolic OH groups and at the aromatic nuclei, and, depending on the number of monomeric units (n) in the macrocyclic structure, they present different size, shape and conformational properties. The regio- and stereoselective control in the fuctionalization of calix[4]- and calix[6]arenes here reported, provides the fundamental synthetic tools to model the shape of these macrocycles and allows one to obtain receptors able to recognize cations, anions, and neutral molecules. The high preorganization and the high complementarity with the guests that can be achieved with calixarene-based hosts make these macrocycles a rich source for molecular receptors.