Crown ethers form complexes not only with simple alkali metal cations but also with ammonium ions and the conjugate acids of primary amines. Much work has been done to refine the selectivity of the ligand to the extent that selection between enantiomers of chiral primary amines is now possible.'A ligand that discriminates enantiomers must itself be chiral, a good example2 being 1. The binaphtyl moieties are asymmetric due to hindered rotation ...
