RIGIDIFICATION OF THE CONE CONFORMATION OF P-TERT-BUTYLCALIX[4]ARENE WITH CARBAMATE GROUPS ON THE LOWER RIM

The conformation of a p-tert-butylcalix[4]arene with four (R)-1(1-phen yl-ethyl)carbamic acid ethoxyester residues on the lower rim has been investigated by X-ray diffraction and H-1 NMR analysis. The molecule a dopts a pinched cone conformation in the solid state with intramolecul ar hydrogen bonding between the carbonyl groups and the nitrogen atoms of proximal carbamate podands. The NMR evidence indicates that this c onformation persists in solution at room temperature. At temperatures >80 degrees C the NMR spectrum is that of a time-averaged C-4v symmetr ical cone conformation.