Rigidification of the Cone Conformation of p-tert-Butylcalix[4]arene with Carbamate Groups on the Lower Rim

Abstract

The conformation of a p-tert-butylcalix[4]arene with four (R)-1(1-phenyl-ethyl)carbamic acid ethoxyester residues on the lower rim has been investigated by X-ray diffraction and ¹H NMR analysis. The molecule adopts a pinched cone conformation in the solid state with intramolecular hydrogen bonding between the carbonyl groups and the nitrogen atoms of proximal carbamate podands. The NMR evidence indicates that this conformation persists in solution at room temperature. At temperatures >80°C the NMR spectrum is that of a time-averaged C_4v symmetrical cone conformation.

Key Words:

• Calix[4]arene carbonate
• pinched cone conformation
• intramolecular H-bonding