Synthesis of Cone, Partial-Cone, and 1,3-Alternate 25,27-Bis[1-(2-ethyl)hexyl]- and 25,27-Bis[1-(2-tert-butoxy)ethyl]calix[4]arene-crown-6 Conformers as Potential Selective Cesium Extractants

The preparation of 25,27-bis[1-(2-ethyl)hexyl]- and 25,27-bis[1-(2-tert-butoxy)ethyl]calix[4]arene-crown-6 combining one polyether crown-6 and one alkylchain O-attached on each side of a calix[4]arene in the cone, partial-cone, and 1,3-alternate conformations are reported. The control over 25,27-bisalkylcalix[4]arene-crown-6 conformation via varying specific reaction conditions was studied. The series of calix[4]arenes have been prepared by two routes, which differ in the order in which the alkyl or polyether groups were introduced. Moreover, methods have been developed to selectively prepare the cone and partial-cone conformers by using an appropriate base in the alkylation reactions. The conformations of these new derivatives have been probed by 1H NMR analysis and X-ray crystallography. The 1H and 13C NMR spectra of 25,27-bis[1-(2-ethyl)hexyl]calix[4]arene-crown-6, 1,3-alternate 1, cone 2, and partial-cone 3 are also discussed.