The Synthesis and Conformational Studies of Chiral Calix[6]arene Derivatives Bearing Amino Acid Ester Residues

Chiral calix[6]arene derivatives were synthesized by the reactions of N-chloroacetyl amino acid ester and 1,3,5-trimethoxy-p-tert-butylcalix[6]arene in the presence of K2CO3. The self-inclusion of the anisole methoxy groups into the calix-cavity stabilizes the compounds in the major flattened cone conformer as shown by their 1H NMR spectra. The larger substituents on the 2,4,6-positions have larger contributions to the stabilities of the compounds. The theoretical calculations by Molecular Force Field Method furthermore indicate that they are prone to exist in a flattened cone conformation.