Synthesis and Assembly of Self-Complementary Calix[4]Arenes

A calix[4]arene was designed to reversibly dimerize and form an egg-shaped enclosure. Adhesive interactions in the assembly were provided by four self-associating ureas, which form a cyclic array containing 16 hydrogen bonds. The synthesis was completed in four steps from the previously described O,O',O'',O'''-tetrabenzylcalix[4]arene. Evidence for dimerization of the calixarene tetraurea was provided by1H NMR, mass spectrometry, and the observation of encapsulated molecules. The resulting cavity was of sufficient size to capture guests such as ethyl benzene and p-xylene.