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Removal of Nitrogen from Azides

A New Chiral and H-NMR Tagging Reagent for ee Analysis of Chiral Azides [Pg.23]

We found that the C3 chiral pro-azaphosphatrane li is an excellent tagging agent for the direct determination of enantiomeric excesses of chiral azides using both P- and H-NMR spectroscopy [121]. Thus the reaction in Eq. (13) is carried out in an NMR tube at 50 °C for 2 hours, followed by NMR spectroscopic analysis. The excellent separations of the P-NMR chemical shifts (ca 1 ppm) allowed the ratios of the diastereomeric imidophosphorane derivatives to be easily measured and these ratios were very close to the expected values for commercially purchased racemic and chirally pure compounds as well as various mixtures of two enantiomers. These ratios were also in good agreement with those measured by H-NMR spectroscopic integration of the proton shifts in the tagged product [see Eq. (13)]. [Pg.23]

It is of interest that the commercially available chiral phosphoramide shown in Fig. 7, when employed in comparison reactions, afforded no observable diastereomeric differentiation either by P- or H-NMR spectroscopy [121]. This result may be rationalized on the fact that the monocyclic reagent has only two chiral centers while li possesses three. Moreover, the chiral centers in li are held rigidly in place, thus perhaps providing an enhanced chiral phosphorus environment. [Pg.23]


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