Determining the Enantiomeric Excess and Absolute Configuration of In Situ Fluorine-Labeled Amines and Alcohols by F-19 NMR Spectroscopy

Abstract

The determination of the enantiomeric excess and absolute configuration of chiral compounds is indispensable in synthetic, pharmaceutical, and biological chemistry. In this article, we describe an efficient F-19 nuclear magnetic resonance (NMR)-based analytical protocol for determining the enantiomeric excess and absolute configuration of in situ fluorine-labeled amines and alcohols. 2-Fluorobenzoylation was used to convert analytes to fluorinated amides or esters. The resulting F-labeled analytes were mixed with a cationic cobalt(III) complex, [Co]BArF, resulting in clean baseline peak separations of analyte enantiomers in F-19{H-1} NMR spectra. The measured Delta delta(RS) signs were unambiguously used to correlate the absolute configurations of amines, amino alcohols, and alcohols. Moreover, the structure-dependent F-19{H-1} NMR signals enabled absolute configuration determination by analyzing the relative chemical shifts of enantiopure analyte samples with [Co]BArF and ent-[Co]BArF.