Metal Selectivity of Conformational Isomers Derived from p-t-Butylcalix[4]arene

Abstract “Cone” and “partial cone” isomers of 25,27-bis(2-pyridylmethoxy)-26,28-bis(ethoxycarbonylmethoxy)-p-t-butylcalix[4]arene (3) were isolated by a TLC method and the structures were identified by 1H NMR. From two-phase solvent extraction of alkali picrates, the size of the ionophoric cavities was estimated to be in the order, partial-cone-3 > tetrakis(ethoxycarbonylmethoxy)-p-t-butylcalix[4]arene (cone) > cone-3. This is the first quantitative estimation of the ionophoricity of conformationally-isomeric calix[4]arenes.