Question

The following enantiomer of a chiral epoxide is an intermediate in the synthesis of the insect pheromone frontalin. CC1(C)COC(C)(C)CO1 Using the Sharpless epoxidation, show how this enantiomer can be prepared from an allylic alcohou. Uriess cthenwise noted all at on this page (D Cargage Leaming 2013

Short answer

Question: Explain how the enantiomer of a chiral epoxide can be prepared from an allylic alcohol using the Sharpless epoxidation reaction. Answer: The enantiomer of a chiral epoxide can be prepared from an allylic alcohol using the Sharpless epoxidation reaction through a stereoselective process involving a titanium-lewis acid catalyst, an enantiopure ligand, and tert-butyl hydroperoxide as the oxidizing agent. This allows the transformation of the allylic alcohol into the desired chiral epoxide with controlled stereochemistry, which is useful for the synthesis of complex biologically active molecules.

Step-by-step solution

Understanding the Sharpless Epoxidation

The Sharpless epoxidation is a chemical reaction used to transform allylic alcohols into their corresponding epoxy alcohols. It is a highly stereoselective reaction that takes advantage of ligand-accelerated catalysis, using a titanium-lewis acid catalyst and an enantiopure ligand to control the stereochemistry of the transformation. Oxidation is achieved using tert-butyl hydroperoxide, which transfers an oxygen atom to create the epoxide.

Determine the Starting Allylic Alcohol

To determine the starting allylic alcohol, we have to analyze the structure of the target epoxide. Based on the given epoxide structure CC1(C)COC(C)(C)CO1, one can remove the epoxide group and replace it with an OH group on a double bond as follows: CC1(C)CC(C)(C)CO1C=C. This allylic alcohol will then undergo the Sharpless epoxidation to give the desired enantiomer of the chiral epoxide.

Apply the Sharpless Epoxidation Reaction

Now that we have identified the starting allylic alcohol, we can apply the Sharpless epoxidation reaction to generate the desired enantiomer of the chiral epoxide. The reaction conditions for the Sharpless epoxidation are as follows: 1. A catalytic amount of a chiral ligand (e.g., diethyl tartrate) bound to a titanium-based lewis acid (e.g., titanium tetraisopropoxide). 2. An oxidizing agent like tert-butyl hydroperoxide. The overall reaction can be described as: allylic alcohol + Ti(Oi-Pr)4 + chiral ligand + t-BuOOH -> chiral epoxide + (spent catalyst) In our specific case: CC1(C)CC(C)(C)CO1C=C + Ti(Oi-Pr)4 + chiral ligand + t-BuOOH -> CC1(C)COC(C)(C)CO1 + (spent catalyst)

Summary

In conclusion, the Sharpless epoxidation reaction provides a stereoselective way to prepare the enantiomer of the chiral epoxide CC1(C)COC(C)(C)CO1 starting from the allylic alcohol CC1(C)CC(C)(C)CO1C=C. This reaction is an important tool for synthesizing enantiomerically pure epoxides useful for the preparation of complex biologically active molecules.