Synthesis and chiral recognition ability of O-phenyl ethylphosphonothioic acid with a conformationally flexible phenoxy group for CH/π interaction

Enantiopure O-phenyl ethylphosphonothioic acid (1) was easily obtained by the enantioseparation of racemic 1, which was prepared from commercially available phosphorothioic trichloride through four steps. Enantiopure 1 was found to show an excellent chiral recognition ability for various 1-arylethylamine derivatives during the diastereomeric salt formation. Especially, enantiopure 1 could recognize the chirality of oand m-substituted 1-arylethylamine derivatives, of which the chirality is generally difficult to be distinguished by conventional resolving agents. The X-ray crystallographic analyses of the less-soluble diastereomeric salts revealed that the conformation of the phenoxy group in enantiopure 1 could flexibly change in the diastereomeric salt crystals and that the excellent chiral recognition ability of enantiopure 1 resulted from the effective CH/π interaction of the phenoxy phenyl