Crucial Role of Three-Center Hydrogen Bonding in a Challenging Chiral Molecular Recognition

The enantio-discrimination of β-chiral primary ammonium ions is achieved by a rational approach
that utilizes three-center (bifurcated) hydrogen bonding. The extraction experiments on various selected
guests reveal that the bifurcated H-bonding plays a crucial role for the chiral discrimination. The X-ray data
obtained for an inclusion complex substantiate such interactions. Using the bifurcated H-bonding, the chiral
molecular recognition with our C3-symmetric tripodal oxazoline receptors is extended generally toward
ammonium ions of α-, β-, and α,β-chiral amines. Simple molecular models, evoking the bifurcated H-bonding,
explain the chiral discrimination modes.