Question

Question: Epoxidation of the following allylic alcohol using the Sharpess reagent (-)-DET gives two epoxy alcohols in a ratio of 87:13.

1. Assign structures to the major and minor product.
2. What is the enantiomeric excess in this reaction?

Short answer

Answer

a.

b. The enantiomeric excess product is shown below.

Step-by-step solution

Epoxidation

Epoxidation of double bonds can be done in many ways.

Sharpless epoxidation is a method that favors only one product of the possible stereoisomers based on whether the reagent DET is dextrorotatory or leavorotatory during the reaction.

Epoxidation

The addition of oxygen to an alkene forms a cyclic ether known as epoxide (ethylene oxide).

During Sharpless epoxidation, the stereochemistry of the reaction plays a major role.

• (+)-DET causes a bottom face attack on the double bond.
• (-)-DET causes a top face attack on the double bond of the alkene.

Products of the given reaction

The products of the given reaction are shown below.

a.

Sharpless reaction

b. The first product is enantiomeric excess.

Enantiomeric excess epoxide