Calix[4]pyrroles with bulky substituents and their anion binding studies

Calix[4]pyrrole derivatives with bulky substituents at their meso-positions were synthesized via mixed condensation of pyrrole with cyclohexanone and acetophenone derivatives. Anion binding studies, carried out by isothermal titration calorimetry in 1,2-dichloroethane with Cl- and CH3CO2- anions in the form of their tetrabutylammonium salts, revealed that these new calix[4]pyrrole derivatives can bind the aforementioned anions as effectively as the unsubstituted "parent" system, octamethylcalix[4]pyrrole (1). Structural characterizations of new calix[4]pyrroles were carried out by using H-1 and C-13 NMR spectroscopy corroborated with mass spectrometry.