Use of shift reagent with diastereomeric MTPA esters for determination of configuration and enantiomeric purity of secondary carbinols in 1H NMR spectroscopy

Abstract

The relative magnitude of the lanthanide induced shift(LIS)_by Eu(fod) 3 for 1H NMR spectra of the OMe group of diastereomeric ( R)-(+)-α-trifluoromethylphenylacetate esters [( R)-(+)-α-methoxy-α-trifluoromethylphenylacetate esters [( R)-(+)-MTPA esters ( 3)] of thirty-two secondary carbinols have been measured. There is a regularity in the relative magnitudes of the LIS values of the OMe signals of the alternate diastereomers which can be correlated with their absolute configurations. This constitutes a versatile method for assigning absolute configurations to secondary carbinols. Furthermore, the relative intensity of the OMe signals can be used for determination of the composition of these diastereomeric MTPA esters and thus the enantiomeric carbinols from which they are quantitatively prepared. These studies extend the usefulness of MTPA derivatives in stereochemical studies.