Combination of upper‐rim‐1,3‐difunctionalized calixarenes 14, 16, and 18 with tribridged resorcinarenes 4 and 6 and A,C‐di‐bridged resorcinarenes 10 and 13 yields both 1/1 calix‐resorcinarenes (22–24) and 2/1 calix‐resorcinarenes (25, 26). 1/1 Calix‐resorcinarene 22 mainly exists as one conformer (a), but at low temperatures (−60°C) very small amounts ( < 5%) of a second conformer (b) can be observed. Both conformers equilibrate via rotation about one of the C(arene)‐N bonds, with an activation free energy (Δ G≠) of 13 kcal/mol. 2/1 Calix‐resorcinarenes 25 and 26 are more flexible and exist as a mixture of conformers. In order to be able to rigidify the structure of 2/1 calix‐resorcinarenes via rigid spacers between the calixarene fragments, 1,3‐diaminocalixarene derivatives 31, 32, and 34 were synthesized carrying nitro, carboxylic ester, and cyano groups at the unsubstituted aromatic rings. With these calixarene derivatives, three new, functionalized 2/1 calix‐resorcinarenes 35–37 have been synthesized.
Timmerman, P., Boerrigter, H., Verboom, W., & Reinhoudt, D. N. (1995). Synthesis of potential receptor molecules by combination of upper-rim-functionalized calixarenes and partly bridged resorcinarenes. Recueil des travaux chimiques des Pays-Bas, 114(3), 103-111. https://doi.org/10.1002/recl.19951140306