Optical Purity Determination, Conformer Populations, and 1 H NMR Spectral Simplification with Lanthanide Shift Reagents. Part VII: 3,4-Methylenedioxyamphetamine (MDA)

The 60 MHz 1 H NMR spectra of racemic 3,4-methylenedioxyamphetamine (MDA), 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 tris[3-(trifluoromethylhydroxymethylene)- d-camphorato]europium (III), 3. Moderate values of the enantiomeric shift difference, ΔΔδ, were observed for each of the benzylic protons and the CH 3 , with the use of added 3 in CDCl 3 solutions at 28°C. The CH 3 resonance was analytically useful for direct optical purity assays; as little as 3% of the minor enantiomer should be detectable. The (+)-isomer of 1 had its CH 3 absorption at higher field in spectra shifted by 3. Appropriate peak height measurements were determined for best accuracy in optical purity assays. The relative abundances of the different conformers with respect to C α -C β bond rotation based on coupling constants in the CH 2 CH moiety are discussed.