O‐Phosphorylated calix[4]arenes as Li+‐selectivereceptors

Phosphorylation of p‐tert‐butylcalix[4]arene 9 or calix[4]arene 10, having two diethoxyphosphoryl groups at distal positions on their narrow rim (phenolic oxygen atoms), by dibutyloxophosphinechloride or alkylation of 10 by methyl bromoacetate led to the corresponding tetrasubstituted calix[4]arenes 8b–d fixed in a cone conformation. The latter compounds and the similar derivative of calix[4]arene 8a with four diethoxyphosphoryl groups were found to exhibit lithium cation selectivity, which was supported by UV–Vis spectra of THF solutions of the alkali metal picrates and their water–chloroform extraction in the presence of ligands 8a–d. Calculated K /K selectivities range from 2.9 (8d) to 9.5 (8a), which are among the highest values for the calixarene‐based Li+‐selective receptors reported to date.