Synthesis and chiral recognition ability of O-ethyl (2-naphthyl)phosphonothioic acid

Enantiopure O-ethyl (2-naphthyl)phosphonothioic acid 1 was designed on the model of O-ethyl phenylphosphonothioic acid, based on the fact that the chiral recognition abilities of enantiopure mandelic acid and cis-1-aminoindan-2-ol were improved upon by replacing their phenyl/phenylene groups with naphthyl/naphthylene groups, respectively. Enantiopure 1 was easily obtained by the enantioseparation of racemic 1, which was easily synthesized from commercially available 2-bromonaphthalene and diethoxyphosphonothioic chloride, with enantiopure 1-phenylethylamine. Enantiopure 1 showed an excellent chiral recognition ability for several 1-arylethylamine derivatives during the diastereomeric salt formation. The effect of the enlarged aromatic part of 1 is discussed on the basis of X-ray crystallographic analyses.

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(Sp)-O-Ethyl (2-naphthyl)phosphonothioic acidC12H13O2PSEe >99%[α]D21=+10.1 (c 5.4, MeOH)Source of chirality: (R)-phenylethylamineAbsolute configuration: Sp