Enantiodifferentiation of acyclic phosphonium salts in chiral liquid crystalline solutions

The enantiodifferentiation of acyclic phosphonium salts bearing a stereogenic centre, whether on the phosphorus atom or on one of its substituents, was investigated by 2H–{1H}, 13C–{1H} and 31P–{1H} NMR in chiral liquid crystals composed of a polypeptide dissolved in an organic solvent. For the first time, the enantiomers of P-chirogenic phosphorus compounds were discriminated in these anisotropic media, affording good to excellent separation of the signals, allowing the determination of their proportion. While 31P–{1H} NMR spectra showed no chiral separation, 2H–{1H} NMR was efficient in the enantiodifferentiation of an isotopically labelled compound. Better still, 31C–{1H} NMR in chiral liquid crystal appears as a powerful method for the enantiodifferentiation of this class of compounds, since separations of the signal up to 0.8 ppm were observed. In this commercially available anisotropic medium, 2H and 13C NMR offers a new promising alternative method for the enantiodifferentiation of chiral phosphonium salts.

Graphical abstractEnantiodifferentiation of acyclic phosphonium salts was investigated by 2H–{1H} and 13C–{1H} NMR in commercially available chiral liquid crystals. Good to excellent separations allow the determination of ee.Figure optionsDownload full-size imageDownload as PowerPoint slide