ANNELATED CALIXARENES COMPOSED OF CALIX[4]ARENES WITH HYDROXY-GROUPS IN THE ENDO AND EXO POSITION

Various phenol-derived calix[4]arenes (3) bearing four hydroxy groups in the exo position have been prepared by uncatalyzed condensation of suitable dimers or tetramers with formaldehyde in xylene in yields up to 44%. The tetra-tert-butyl compound (3a) has been shown by X-ray ana lysis to adopt a regular cone conformation (nearly identical in shape with the endo isomer) with two intramolecular O-H ... O hydrogen bonds , while the corresponding dimer (6c) prefers a conformation (not possi ble in the calixarene) with two intramolecular O-H ...pi(arene) intera ctions. Condensation of exo-calix[4]arenes 3f,g with free ortho positi ons (easily available by debutylation) with bisbromomethylated dimers gave annelated double (9) and triple (10) calixarenes consisting of en do- and exo-calix[4]arene substructures in yields up to 24% and 10%, r espectively. Molecular dynamics calculations suggest that the exo-cali xarene part in 9 is less mobile than the entirely flexible 3, while th e endo-calixarene part shows a higher mobility than usual. A complete interconversion cone --> cone is impossible, however, which enables th e construction of inherently chiral molecules.