Abstract
The rates of hydrolysis of oxazolidines with ortho-hydroxyphenyl substituents at C(2) are more than 30 times faster than oxazolidines with para-hydroxyphenyl substituents. The later rates are identical to those with a phenyl group at C(2) indicating the ortho-hydroxyl orientation is responsible for the acceleration. In the solid state the ortho-hydroxyl group is hydrogen bonded to the ring nitrogen atom. Since the rate determining step probably involves protonation of the ring oxygen atom and ring cleavage, the rates of reaction are rationalized by a reorientation of the hydrogen bond to the ring oxygen after protonation of the ring nitrogen atom. This involves a movement of less than 1 Å. A bifurcated hydrogen bond is an alternate but related possibility.
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Acknowledgment
We thank NIH (RBW, Grant No. S06 RR0821 1-08) and the TCU Research Fund for their financial support. The authors also thank Dr. Gordon Eggleton at Southeastern Oklahoma State University for some of the NMR spectra and Kyle Greer for recrystallization of compounds.
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Bourne, S.A., Fitz, L.D., Kashyap, R.P. et al. Oxazolidines from the reaction of (-) ephedrine and ( +) pseudoephedrine with salicylaldehyde and p-hydroxybenzaldehyde and their rates of hydrolysis. J Chem Crystallogr 27, 35–44 (1997). https://doi.org/10.1007/BF03543085
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DOI: https://doi.org/10.1007/BF03543085