Sharpless Epoxidation Practice Problems
In an enantioselective (or asymmetric) synthesis an achiral starting material is converted into mostly one enantiomer of a chiral product. For example, in the asymmetric epoxidation developed by K. Barry Sharpless, allylic alcohols are converted to epoxides with more than 90% enantiomeric excess. A typical Sharpless epoxidation uses tert-butyl hydroperoxide, titanium(IV) isopropoxide, and a dialkyl tartrate ester as the reagents, as is shown in the epoxidation of a geraniol derivative below.
(i) Identify the oxidizing agent in this reaction. What is the likely function of the other reagents?
(ii) How can the reaction give just one mostly pure enantiomer of the product?
(iii) Give the structure of the other enantiomer of the product. What reagents will you use to epoxidize the geraniol derivative to produce this other enantiomer?