OXAZOLIDINES FROM THE REACTION OF (-)EPHEDRINE AND (-HYDROXYBENZALDEHYDE AND THEIR RATES OF HYDROLYSIS()PSEUDOEPHEDRINE WITH SALICYLALDEHYDE AND P)

The rates of hydrolysis of oxazolidines with ortho-hydroxyphenyl subst ituents at C(2) are more than 30 times faster than oxazolidines with p ara-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-hyd roxyl group is hydrogen bonded to the ring nitrogen atom, Since the ra te determining step probably involves protonation of the ring oxygen a tom and ring cleavage, the rates of reaction are rationalized by a reo rientation of the hydrogen bond to the ring oxygen after protonation o f the ring nitrogen atom, This involves a movement of less than 1 Angs trom. A bifurcated hydrogen bond is an alternate but related possibili ty.