Enantiodifferentiation by ¹H and ¹³C NMR Spectroscopy (Dirhodium Method) – Selectivity of Oxygen Functionalities

Abstract

Chiral carbonyl compounds can easily be enantiodifferentiated by the dirhodium method. The rhodium atoms reveal a remarkable selectivity in binding to oxygen atoms, which is of great advantage for discriminating chiral polyoxygenated natural products. Amides are the strongest ligands followed by ketones and esters; ethers and alcohols/phenols are even less effective. This sequence is rationalized by electronic charges at the oxygen atoms, as obtained from density functional calculations.

Competition of Ester, Amide, Ether, Carbonate, Alcohol and Epoxide Ligands in the Dirhodium Experiment (Chiral Discrimination by NMR Spectroscopy) [1]

“…Recently, we found in a comparative study that Rh* shows a remarkable binding selectivity when several different oxygenfunctionalities (alcohol, ether, carbonyl, etc.) are present in a molecule [6]. Selectivity is an important feature if various functional groups in a molecule compete for binding to a chiral NMR auxiliary because its absence diminishes diastereomeric differentiation by averaging effects on NMR signals in the various individual adducts.…”