13. Addition to Form Three-Membered Rings: Carbenoids and Epoxidation

Freshman Organic Chemistry II (CHEM 125B)

After drill on the mechanism of the pinacol rearrangement, this lecture applies molecular-orbital analysis to simultaneous electrophilic/nucleophilic attack by a single atom to form a three-membered ring from an alkene. These reactions provide drill in consistent use of the curved-arrow formalism for describing electron-pair shifts. Two alternative mechanisms for formation of cyclopropanes by the alkylzinc Simmons-Smith "carbenoid" reagent are proposed, and the one-step mechanism is supported by theory. Epoxidation of alkenes by peroxycarboxylic acids also seems to go by way of a concerted electrophilic/nucleophilic process involving a single transition state. The stereochemistry and scale of various paths to epoxides is discussed in the context of their commercial utility.

00:00 - Chapter 1. The Pinacol Rearrangement Mechanism
04:36 - Chapter 2. Carbenoids and Simmons-Smith Cyclopropanation
17:56 - Chapter 3. Epoxidation by Peroxycarboxylic Acids
38:40 - Chapter 4. Other Routes to Epoxides
46:44 - Chapter 5. Practical Utility of Epoxides

Complete course materials are available at the Open Yale Courses website: http://oyc.yale.edu

This course was recorded in Spring 2011.