<i>N</i>-Tosylpyrrolidine Calix[4]pyrrole: Synthesis and Ion Binding Studies

The synthesis and preliminary solution phase ion binding properties of the <i>N</i>-tosylpyrrolidine calix[4]pyrrole <b>2</b> are reported. This β-octaalkyl-substituted calix[4]pyrrole, the first to be prepared via a direct condensation reaction, was obtained by reacting the 3,4-alkyl-functionalized pyrrole <b>8</b> with acetone in the presence of an acid catalyst. On the basis of <sup>1</sup>H NMR spectroscopic analyses and isothermal titration calorimetry, it was concluded that, compared with the parent, β-unsubstituted calix[4]pyrrole (<b>1</b>), compound <b>2</b> possesses significantly enhanced binding ability for halide anions in chloroform. Furthermore, <b>2</b> proved capable of solubilizing in chloroform solution the otherwise insoluble salts, CsF and CsCl. These effects are ascribed to the interactions between the four tosyl groups present in <b>2</b> and the counter cations of the halide anion salts.