Microwave-Assisted Synthesis of Bidentate Chiral Unsymmetrical Urea Derivatives of P-tert-butylcalix[4]Arene and their Anion Recognition Properties

Abstract

Four new derivatives of p-t-butylcalix[4]arene containing two (1,3-distal) chiral unsymmetrical urea moieties at the lower rim were synthesised in four steps. Their anion recognition properties toward MeCO₂⁻, H₂PO₄⁻, NO₃⁻, I⁻, Br⁻, Cl⁻ were assessed by UV-Vis titration spectroscopy. All the receptors showed the strongest recognition ability for MeCO₂⁻, one of them having an association constant of 3139 M^-1. ¹H NMR studies of this receptor complex confirmed its tight binding of MeCO₂⁻.