¹H NMR Spectral Simplification with Achiral and Chiral Lanthanide Shift Reagents. Fenimide. Direct Simultaneous Determination of Four Stereoisomers

Abstract

The 60 MHZ ¹H NMR spectra of racemic commercial fenimide, 4-ethyl-3-methyl-3-phenyl-2,5-pyrrolidine-dioner 1, have been studied in CDCl₃ solution at 28° with the achiral shift reagent, tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato) europium-(III) 2, and the chiral reagent, trist3-(heptafluoro-propylhydroxymethy1ene)-d-camphoratol europium(III) 3. Use of 2 substantially increased the chemical shift differences between resonances of corresponding nuclei in the alpha and beta diastereomers, simplifying mixture analyses. Use of the chiral 3 produced enantiomeric shift differences, ΔΔΔ for several signals of 1. In particular, with a 0.309 molal solution of 1 and a 3:1, molar ratio near 0.4, four distinct singlets can be seen for the quaternary methyl signal. Direct simultaneous analysis for all four stereoisomers (two pairs of enantiomers) should be feasible.

Key Words:

• Lanthanide
• NMR Shift Reagent
• Fenimide
• Europium
• Chiral
• Optical Purity
• Enantiomer
• Diastereomer
• 4-ethyl-3-methyl-3-phenyl-2,5-pyrrolidine-dione