DETERMINATION OF THE ENANTIOMERIC COMPOSITION OF CHIRAL Δ-2-OXAZOLINES-1,3 BY¹H AND¹⁹F NMR SPECTROSCOPY USING CHIRAL LANTHANIDE-SHIFT REAGENTS

Determination of the enantiomeric composition of chiral delta‐2‐oxazolines‐1,3 by 1H and 19F NMR spectroscopy using chiral solvating agents

“…The theoretical ee for 1Aa was 62.2%. Using typical conditions for recording onedimensional spectra 11 and a Gaussian window for resolution enhancement, the measured ee was 58.7%, indicating a precision of about ±3% of ee determination. Similar results were obtained with 1Ac (⌬ = 9.9 Hz) and even with 1Ab despite the small ⌬ value (1.4 Hz).…”

“…As expected, C 6 D 6 entails appreciable aromatic solvent induced shifts, ASIS, 33 all the signals being significantly shielded compared to their values in CDCl 3 solution. 11 It is also noteworthy that C 6 D 6 entailed the complication of the four spins system H(4), H(4Ј), H(5), and H(5Ј) of oxazoline 1e, and a second-order AAЈBBЈ system was observed in place of a first-order AAЈXXЈ system. Nevertheless, this drawback is not critical as, in the perspective of enantiomeric discrimination, the best expected analytical nuclei are rather the CH 2 (6), CH(6) and CH 3 -C(4), CH 3 -C(5) or CH 3 -C(6) protons than the AAЈBBЈ or ABX ones.…”

“…The nitrogen N(3) was previously proven to be the privileged site for complexation with the lanthanide Lewis acidic center of CLSRs. 11,12 Moreover, the relatively rigid fivemembered ring and the closeness of the chiral center [C(4) or C(5) for 1Aa-d or 1Ba, and C(6) for 1e] from the basic solvating sites are, with the presence of an aromatic substituent, molecular characteristics that provide a sufficient number of interactions with the CSA 5 that is stipulated by Dalgleish 13 and later by Pirkle et al 14 as the requisite condition for enantiomeric discrimination. As alcoholic CSAs, 1-phenyl-2,2,2-trifluoroethanol 5a, 1-(␣-naphthyl)-2,2,2-trifluoroethanol 5b, and 1-(9-anthryl)-2,2,2-trifluoroethanol) 5c have extensively been used for the enantiomeric discrimination of chiral amines, 15 ␤-ethanolamines, 16 oxaziridines, 17 oxadiazines, 18 and even oxazolines.…”

“…1B) and recently we succeeded in their enantiomeric discrimination using chiral lanthanide shift reagents (CLSRs) during 1 H or 19 F NMR analysis. 11 In order to apply the most convenient chiral technique to the extracts of biological insect tissues incubated by the substrates 1, we are presently checking other analytical methods and particularly the use of chiral solvating agents (CSAs) of the trifluoromethyl carbinol type 5a,c (Fig. 1B).…”

NMR-based Enantiodifferentiation of Chiral trans-2-Phenylcyclopropane Derivatives Using a Chiral Lanthanide Shift Reagent

“…Care is required in determining absolute configurations based on empirical correlations of chemical shifts in the presence of chiral shift reagents. While several studies have determined absolute configurations based on ΔΔδ, [11][12][13][14][15][16][17][18][19] there are cases in which the sign of ΔΔδ changes within the same series of compounds. 20,21 In the current study, absolute configurations are considered accurate because the differences in the patterns of R and S enantiomeric methyl chemical shifts (ΔΔδ) were the same (i.e., the downfield chemical shift of the S enantiomer matches the upfield chemical shift of the R enantiomer).…”