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.