Stereochemistry of the Spontaneous, Acid-Catalyzed and Base-Catalyzed Hydrolyses of Styrene Oxide

Abstract

The stereochemical courses of the spontaneous, hydronium ion-catalyzed and hydroxide ion-catalyzed hydrolyses of (R)-styrene oxide have been determined by 1H NMR analysis of the bis-(+)-α-(methoxy-α-trifluoromethyl)phenylacetate diesters of the styrene glycol products from each reaction. The glycol product from the spontaneous reaction of chiral styrene oxide is the result of 93% inversion and 7% retention. This result, coupled with published results of 18O-labeling experiments, indicates that essentially all of the styrene oxide that reacts with cleavage of the benzyl C-O bond yields glycol with inversion of stereochemistry at the benzyl carbon. A mechanism involving addition of neutral water concerted with benzyl C-O bond breaking is proposed for this reaction. The glycol product from the acid-catalyzed reaction was determined to be the result of 67% inversion and 33 % retention at the benzyl carbon. This result, which agrees with one previous publication and contradicts that of another, reflects the stereochemistry of addition of solvent to the benzyl carbon. Consistent with a recent report that 18O-hydroxide attacks the α- and β-carbons of styrene oxide at almost equal rates, styrene glycol from the reaction of chiral styrene oxide with sodium hydroxide was found to be, within experimental error, completely racemic. © 1994 American Chemical Society.