Calix[4]tubes: an approach to functionalization.

Adamantylcalix[4]arenes decorated with ester groups and calix[4]arene tetratosylates were used to prepare a series of calix[4]tubes bearing 3-methoxycarbonyl- and 3-methoxycarbonylmethyl-1-adamantyl units (up to eight) in good yield. These compounds were subjected to further chemical transformations giving a wide set of novel ester-, acid-, hydroxy-, amine-, and urea-functionalized calix[4]tubes. Introduction of urea groups into the calixtube core led not only to anion-targeted receptors, but also provided heteroditopic behavior of the hosts, which enriches the well-established potassium-uptake ability of calix[4]tubes.