Resorcinarene

A resorcinarene (also resorcarene or calix[4]resorcinarene) is a macrocycle, or a cyclic oligomer, based on the condensation of resorcinol (1,3-dihydroxybenzene) and an aldehyde. Resorcinarenes are a type of calixarene.

Resorcinarenes interact with other molecules forming a host-guest complex. Resorcinarenes and pyrogallolarenes self-assemble into to larger supramolecular structures. Both in the crystalline state and in organic solvents, six resorcinarene molecules are known to form hexamers with an internal volume of around one cubic nanometer (nanocapsules) and shapes similar to the Archimedean solids.Hydrogen bonds appear to hold the assembly together. A number of solvent or other molecules reside inside. The resorcinarene is also the basic structural unit for other molecular recognition scaffolds. A number of molecular structures are based on this macrocycle, namely cavitands and carcerands.

The resorcinarene macrocycle is typically prepared by condensation of resorcinol and an aldehyde in concentrated acid solution. Recrystallization typically gives the desired isomer in quite pure form. However, for certain aldehydes, the reaction conditions lead to significant by-products. Therefore, alternative condensation conditions have been developed, including the use of Lewis acid catalysts.

A green chemistry procedure was recently developed using solvent-free conditions: resorcinol, an aldehyde, and p-toluenesulfonic acid are ground together in a mortar and pestle at low temperature. A paste-like solid forms upon sitting for several minutes, which can be washed with water and crystallized to give the desired resorcinarene.

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