Enantiopure cyclic O-substituted phenylphosphonothioic acid: synthesis and chirality-recognition ability

As a new acidic selector (resolving agent), we synthesized an enantiopure O-alkyl phenylphosphonothioic acid with a seven-membered ring ((R)-5), which was designed on the basis of the results for the enantioseparation of 1-arylethylamine derivatives with acyclic O-ethyl phenylphosphonothioic acid (I). The phosphonothioic acid (R)-5 showed unique chirality-recognition ability in the enantioseparation of 1-naphthylethylamine derivatives, aliphatic secondary amines, and amino alcohols; the ability was complementary to that of I. The X-ray crystallographic analyses of the less- and more-soluble diastereomeric salts showed that hydrogen-bonding networks in the salt crystals are 2(1) -column-type with a single exception which is cluster-type. In the cases of the 2(1) -column-type crystals, stability of the crystals is firstly governed by hydrogen bonds to form a 2(1) -column and secondly determined by intra-columnar T-shaped CH/π interaction(s), intra-columnar hydrogen bond(s), inter-columnar van der Waals interaction and/or inter-columnar T-shaped CH/π interaction(s). In contrast, the cluster-type salt crystal is stabilized by the assistance of inter-cluster T-shaped CH/π and van der Waals interactions. To realize still more numbers of intra- and inter-columnar and -cluster T-shaped CH/π interactions, the seven-membered ring of (R)-5 plays a considerable role.