CHEM 125b - Lecture 13 - Addition to Form Three-Membered Rings: Carbenoids and Epoxidation

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

Overview

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.

Resources

Professor McBride's website resource for CHEM 125b (Spring 2011)

https://webspace.yale.edu/chem125/

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