Synthesis and alkali metal picrate extraction studies of lower rim functionalized p-tert-butylcalix[4]arene crown ethers

The syntheses of four new calix[4]arene receptors, i.e. , each of which contains an oxahexacyclic cage moiety, are reported. The structures of two of these receptors, i.e. and , have been established via single crystal X-ray structural analysis. The complexation properties of were determined via a series of alkali metal picrate extraction experiments. Two of the cage-functionalized calix[4]arene-crown-5 hosts, i.e. and , display somewhat greater extraction avidity toward Na+ picrate vis-à-vis the remaining alkali metal picrates. By way of contrast, host systems and function effectively as a moderately selective K+ extractants and display significantly increased extraction avidity toward K+ picrate vis-à-vis and .