Synthesis of C3v-Symmetrical 1,3,5-Tris-Protected Calix[6]arene-Based Molecular Platforms

Few synthetic methodologies that yield tris-functionalized C3v-symmetrical calix[6]arenes have been reported. In this work, three allyl protecting groups are selectively placed in 1,3,5 alternate positions of three pristine calix[6]arenes, each differing by their substituent on the large rim, resulting in three new C3v-symmetrical molecular platforms. Removal of the protecting allylic groups gives access to sophisticated calix[6]arenes that can be further modified. The potential of these new C3v-symmetrical molecular platforms is notably exemplified through the development of a new family of calix[6]arene-based N ligands.

The synthesis and characterization of giant Calixarenes

Calixarenes are cyclic oligomers obtained by condensation of suitable p-functionalised phenols with formaldehyde, usually allowing for the synthesis of the well known small calixarenes (including up to eight phenolic subunits). We report here the discovery of much larger members of this family, exhibiting sizes up to 90 phenolic subunits: the giant calixarenes. These macrocycles are obtained according to simple, easily scalable processes, in yields up to 65%. We show that the formation of these giant macrocycles is favored by an oxygen-containing-group at the para-position of the starting phenol, high concentrations of heavy alkaline bases (rubidium or cesium hydroxides) and long reaction times. A mechanism is proposed to rationalize these observations. These giant macrocycles can also be obtained in the quasi-solid state, opening interesting perspectives in the field of calixarenes chemistry. Along with their intrinsic fundamental interest, these objects are also opening interesting applicative potentialities.