Optical purity determination and 1H-NMR spectral simplification with lanthanide shift reagents — VIII. An indacrinone precursor, 6,7-dichloro-5-methoxy-2-methyl-2-phenyl-1-indanone

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The 60 MHz 1H NMR spectra of racemic 6,7-dichloro-5-methoxy-2-methyl-2-phenyl-1 indanone ( 1) have been studied 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 reagents, tris[3-(trifluoromethylhydroxymethylene)- d-camphorato] europium (III) ( 3) and tris[3-(heptafluoropropylhydroxymethylene)- d-camphorato] europium (III) ( 4). While some enantiomeric shift differences, ΔΔδ, were seen for some protons of 1 with 3, dramatically larger values were obtained with 4. The latter would be the reagent of choice for direct optical purity determinations of 1 using the 2-methyl resonance. Optimum conditions would use a 4:1 molar ratio of 0.1–0.25, providing near-baseline resolution for the peaks and freedom from overlap with interfering peaks. Less than 3% of the minor enantiomer should be detectable. The results are consistent with lanthanide complexation at the carbonyl. The value of ΔΔδ for the C 2 methyl of 1.1 ppm with a 4:1 molar ratio of 1.50 appears to be among the highest reported values for simple ketones with 3 or 4.