Addition of chiral arylperfluoroalkylcarbinols to solutions of oxaziridines causes the NMR spectra of the oxaziridine enantiomers to be nonidentical. The resultant chemical shift differences allow direct determination of the enantiomeric composition of the oxaziridine and may ultimately allow assignment of absolute configuration to each enantiomer. Reasons underlying the origin of the spectral nonequivalence are discussed and absolute specific rotations for several oxaziridines are presented.Oxaziridines (1) have attracted considerable stereochemical attention as a consequence of the dissymmetric nitrogen and its appreciable barrier to inversion. Optically active oxaziridines have been prepared by the oxidation of achiral imines with chiral peracids,' by the oxidation of chiral imines with achiral peracids,2 by thermal isomerization in a chiral liquid crystal,3 and by photochemical synthesis in a chiral solvent.4 The enantiomeric purities of most chiral oxaziridines have been unknown, since only in select instances have partially resolved oxaziridines been crystallized to enantiomeric purity so that absolute specific rotations might be determined.We now report a method employing chiral solvating agents (CSA) for the rapid and convenient NMR determination of the enantiomeric composition of oxaziridines. This method may ultimately allow determination of oxaziridine absolute configuration as well.When used as CSA, fluoro alcohols of general structure 2 cause the NMR spectra of oxaziridine enantiomers to differ. This behavior was first noted5 when oxaziridine la, formed by oxidation of N-tert-butylformimine with ( S ) -( +)-monoperoxycamphoric acid (MPCA), was examined by NMR in the presence of (R)-(-)-2,2,2-trifluoro-l-phenylethanol ( l a ) and separate tert -butyl singlets and AB patterns were observed for each oxaziridine enantiomer. Simply by comparing the relative signal intensities, the enantiomeric composition of la was determined.The differential NMR effect of CSA (2b) upon the enantiomers of partially resolved oxaziridine l b is shown in Figure 1. Results obtained from the NMR spectra of other partially resolved oxaziridines in the presence of (S)-(+)-2b and 2c are shown in Table I. In each instance, enantiomeric composition was determined from the relative intensities of the anisochronous resonances of the enantiomers. l a , R' = R" = H; R = tert-butyl b, R' = H; R" = CH,; R = tert-butyl B A r t O H Rf 2a, Ar = phenyl; Rf = CF, b, Ar = 9-( 10-methylanthryl); Rf = CF, c, Ar = 9-anthryl; Rf = CF, d, Ar = 9-(10-Bromoanthryl); Rf = CF, Type 2 CSA cause enantiomeric spectral nonequivalence for a wide variety of solutes by forming diastereomeric chelate-like solvates, exemplified by generalizations 3a,b. These diastereomeric solvates have nonidentical time-averaged NMR spectra owing to the stereochemical dependence of the shielding effect exerted by the aromatic substituent of 2 on R1 and Rz. Typically R1 and R2 show opposite senses of non-equivalence. In alkyl oxaziridines there are but two basic sites, the oxy...