The synthesis of the A,D-m-xylylene-bridged B,C,E,F-tetra-O-alkylcalix[6]arenes 1b–c and the A,D-B,C;E,F-triply bridged calix[6]arenes 2a-c is described. The cone conformation of the new bridged calix[6]arenes has been established by a full set of 1D/2D 1H and 13C NMR techniques. These compounds are substantially more rigid than calix[6]arene analogues with an A,D-p-xylylene bridge, and the resulting cavities are better defined. Molecular mechanics optimization of triply bridged calix[6]arenes 2b and 2c resulted in structures fully consistent with the NMR spectra.
![Conformational control of calix[6]arenes through multiple bridges](https://www.iciq.org/wp-content/uploads/2014/03/Conformational-control_eng_noticies_articles_2005_12.jpg)