Synthesis, structure, and anion binding of functional oxacalix[4]arenes

Abstract

Oxacalix[4]arenes obtained from the highly efficient, one-pot S_NAr reaction were post-macrocyclization functionalized through the reduction of nitro groups and hydrolysis of the ester groups to obtain several derivatives of desired solubility. The difficulties in basic hydrolysis of ester groups were overcome via developing an acid hydrolysis method for tert-butyl ester derivatives of this class. The synthesis of symmetrical oxacalix[4]arenes from an unsymmetrically substituted precursor was also explored via a multiple step fragment coupling approach. Compounds 17 & 18 adopted 1,3-alternate conformations in the solid state as most oxacalix[4]arenes did, and a chair (zigzag) conformation was revealed for tetraamido oxacalix[4]arene (6a) by X-ray single crystal analysis. The tetraureido oxacalixarene (7) showed strong association towards various anions such as F⁻, Cl⁻, Br⁻, I⁻, Ac⁻, and HSO₄⁻ with a 1 : 1 stoichiometry as revealed by ¹H NMR analysis and UV-vis measurements.