Configurational assignment of vic-amino alcohols from their circular dichroism spectra with dirhodium tetracetate as an auxiliary chromophore

The circular dichroism spectra of a variety of vic-amino alcohols in the presence of dirhodium tetraacetate as an auxiliary chromophore were measured in ethanol as the solvent. The method was tested with several model compounds, representing both acyclic and cyclic amino alcohols, including biologically important adrenergic drugs as well as amino sugars. The study demonstrated that the sign of the Cotton effects is determined by the preferred helicity of the O–C–C–N unit in the chiral complex formed in situ. The combined analysis of the CD, UV–vis, 1H and 13C NMR indicated predisposition to form chiral complexes by initial coordination of the amino alcohol at the axial coordination site followed by migration to the equatorial position. Finally, after migration of the ligand to an equatorial position(s) a bridging or a chelating complex is formed. Hence, vic-amino alcohols in ethanol act as bidentate ligands in the end.

Graphical abstractCD spectra of vic-amino alcohols with Rh2(OAc)4 acting as an auxiliary chromophore in ethanol show three prominent bands in the 450–280 nm spectral region. The study demonstrated that the sign of these Cotton effects is determined by the helicity of the O–C–C–N unit in preferred conformation adopted by the ligand in the chiral complex formed in situ.Figure optionsDownload full-size imageDownload as PowerPoint slide