ASYMMETRICALLY SUBSTITUTED CALIX[4]ARENES - A 2-DIMENSIONAL H-1-NMR STUDY OF A TETRAESTER DERIVATIVE IN THE CONE-CONFORMATION

Several new chiral calix[4]arenes with three or four different substituents in the p-position have been prepared by fragment condensation. Standard derivatization procedures always led to the formation of mixtures of various conformational isomers from which the derivative in the cone-conformation could be isolated only by preparative HPLC. For a tetraester derivative it was shown by two-dimensional H-1 NMR spectroscopy, that due to the different substituents the cone-conformation is strongly distorted. The sodium complex of this tetraester, however, assumes a regular cone-conformation again.