STEREOCHEMISTRY OF THE SPONTANEOUS, ACID-CATALYZED AND BASE-CATALYZEDHYDROLYZES OF STYRENE OXIDE

The stereochemical courses of the spontaneous, hydronium ion-catalyzed and hydroxide ion-catalyzed hydrolyses of (R)-styrene oxide have been determined by H-1 NMR analysis of the alpha-(methoxy-alpha-trifluorom ethyl)phenylacetate diesters of the styrene glycol products from each reaction. The glycol product from the spontaneous reaction of chiral s tyrene oxide is the result of 93% inversion and 7% retention. This res ult, coupled with published results of O-18-labeling experiments, indi cates that essentially all of the styrene oxide that reacts with cleav age of the benzyl C-O bond yields glycol with inversion of stereochemi stry at the benzyl carbon. A mechanism involving addition of neutral w ater concerted with benzyl C-O bond breaking is proposed for this reac tion. The glycol product from the acid-catalyzed reaction was determin ed to be the result of 67% inversion and 33% retention at the benzyl c arbon. This result, which agrees with one previous publication and con tradicts that of another, reflects the stereochemistry of addition of solvent to the benzyl carbon. Consistent with a recent report that O-1 8-hydroxide attacks the alpha- and beta-carbons of styrene oxide at al most equal rates, styrene glycol from the reaction of chiral styrene o xide with sodium hydroxide was found to be, within experimental error, completely racemic.