Resorcinarene-derived cavitands

The first deep-cavity cavitand to be synthesized was the 2.3-quinoxaline derivative 4 (Fig. 4). This second row of aromatic rings in this cavitand. and related cavitands formed by the condensation of resorcinarenes with 2,3-dichloropyrazines. is conformationally flexible. Thus, they exist in a range of conformers between the vaselike C4v form (shown) and a flat C21 form. These families of compounds were termed velcrands, because in the flat, "kite-like" form, they have a propensity to dimerize.When not binding themselves, these types of cal-itands also bind mono-" or di-substituted"benzene derivatives. 

An alternative to deepening the cavity in the manner of cavitand 4 comes in the form of the stereoselective bridging of resorcinarenes. The first successes in this regard were carried out with a number of phosphorus derivatives, e.g., Stereoselective bridging with... 

Functionalization of resorcinarenes involves three primary routes (1) At the R-groups or feet of the resorcinarene by choice of aldehyde in the resorcinarene reaction, and/or post-macrocyclization modification (2) the 2-position (X, Scheme 9.1) can be controlled by choice of the starting resorcinol derivative or modification of the resorcinarene product (3) functionalized through utilization of the phenolic groups at the upper rim. A variation of this strategy, using bis-electrophiles that bridge the phenolic pairs, leads to the cavitands discussed here. 

Here we summarise the results of a comparative study on the gas-solid and gas-liquid interactions between two classes of cavitand receptors derived from resorcinarenes and a series of organic vapors using mass sensitive QCM (Quartz Crystal Microbalance) sensors. 

Pietraszkiewicz has investigated the interaction of L-sorbose, o-glucose, d-galactose and o-cellobiose with Langmuir films of boron-containing cavitands derived from calix[4]resorcinarenes. Binding could be detected but, they were unable to make any conclusions regarding the stereochemistry or stoichiometry of the complexes formed. 

---