Relative Configuration and Conformation of 5-(Dimethoxyphosphoryl)-2-methoxy-1,2λ5-oxaphospholan-2-ones by Multinuclear NMR Spectroscopy

Information on the hitherto unknown relative configuration and on the conformation of the title compounds in solution can be derived from nuclear Overhauser effects and coupling constants. Whereas the bridged 5-(dimethoxyphosphoryl)-2-methoxy-1,2λ⁵-oxaphospholan-2-ones 6 and 7 are sterically strained and, therefore, conformationally rigid, the C(3)-unsubstituted compound 1 does not show a preferred solution conformation. Phenyl substituents at C(3) (compounds 2 – 5 ) tend to adopt a pseudoequatorial position, this way leading to a definite conformation of the respective compounds. The influence of the conformation on the NMR spectra is discussed. ³¹P-NMR Spectroscopy is ideally suited for the characterization and quantification of the isomers 2 – 5 present in the reaction mixture.