Calix[5]arene‐Based Molecular Vessels for Alkylammonium Ions

Calix[5]arenes locked in a C5v-symmetric cone conformation (depicted schematically on the right as a truncated pyramid) provide highly preorganized cavities for the formation of strong 1:1 inclusion complexes with linear alkylammonium ions; the nBuNH3+/tBuNH3+ selectivity is up to 103. These calixarenes also act as biomimetic host systems towards specific amino acid methyl esters and display an enzymelike selectivity. R is, for example, Me, CO2Me.