The Prediction of the Absolute Stereochemistry of Primary and Secondary 1,2-Diols by 1H NMR Spectroscopy: Principles and Applications

The absolute configuration of 1,2‐diols formed by a primary and a secondary (chiral) hydroxyl group can be deduced by comparison of the 1H NMR spectra of the corresponding (R)‐ and bis‐(S)‐MPA esters (MPA=methoxyphenylacetic acid). This method involves the use of the chemical shifts of substituents L1/L2 attached to the secondary (chiral) carbon, and of the hydrogen atom linked to the chiral center (CαH) as diagnostic signals. Theoretical (AM1, HF, and B3 LYP calculations) and experimental data (dynamic and low‐temperature NMR spectroscopy, studies on deuterated derivatives, constant coupling analysis, circular dichroism (CD) spectra, and NMR studies with a number of diols of known absolute configuration) prove that the signs of the ΔδRS obtained for those signals correlate with the absolute configuration of the diol. A graphical model for the reliable assignment of the absolute configuration of a 1,2‐diol by comparison of the NMR spectra of its bis‐(R)‐ and bis‐(S)‐MPA esters is presented. The absolute configuration of 1,2‐diols formed by a primary and a secondary (chiral) hydroxyl group can be deduced by comparison of the 1H NMR spectra of the corresponding (R)‐ and bis‐(S)‐MPA esters (see graphic; MPA = methoxyphenylacetic acid).