In this article we describe the selective O-benzylation of para-unsubstituted calix[6]arene 1 in rings 1 and 4 (2a-c) and the subsequent alkylation of phenol groups with -haloesters (methyl esters 3a, 3c, and 3e; tert-butyl esters 3b, 3d, and 3f) to determine the effect of these groups on their conformational behavior. 2D NMR studies at 188 K reveal that compounds 2a-c, 3b, 3d, and 3f are less flexible, showing a 1,2,3-alternate conformation. The same conformation has been observed in the solid state.
![Synthesis and conformational studies on hexa-O-alkyl p-unsubstituted calix[6]arenes](https://www.iciq.org/wp-content/uploads/2014/03/Synthesis-and-conformational_eng_noticies_articles_2005_4.gif)