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 in four steps. Enantiopure 1 was found to show an excellent chiral recognition ability for various 1-arylethylamine derivatives during the diastereomeric salt formation. In particular, enantiopure 1 was able to recognize the chirality of o- and m-substituted 1-arylethylamine derivatives, of which the chirality is generally difficult to establish by conventional resolving agents. X-ray crystallographic analyses of the less-soluble diastereomeric salts revealed that the conformation of the phenoxy group in enantiopure 1 could 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 group.

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(Rp)-O-Phenyl ethylphosphonothioic acidC8H11O2PSEe >99%[α]D20=-9.9 (c 1.23, MeOH)Source of chirality: (R)-phenylethylamineAbsolute configuration: Rp