Return to Contents  Chapter 20: Carboxylic Acid Derivatives. Nucleophilic Acyl Substitution  Ch 20 contents

Reactions of RLi and RMgX with Esters
(review of Chapter 14)

reaction of RLi or RMgX with esters
Reaction usually in Et2O followed by H3O+ work-up

Reaction type:  Nucleophilic Acyl Substitution then NucleophilicAddition

Summary

MECHANISM OF THE REACTION OF RMgX WITH AN ESTER

Step 1:
The nucleophilic C in the organometallic reagent adds to theelectrophilic C in the polar carbonyl group of the ester. Electrons from the C=O move to the electronegative O creating thetetrahderal intermediate, a metal alkoxide complex.
addition of Grignard reagent to an ester
Step 2:
The tetrahedral intermediate collapses and displaces the alcohol portion of the ester as a leaving group, in the form of the alkoxide, RO-.This produces a ketone as an intermediate.
Step 3:
The nucleophilic C in the organometallic reagent adds to the electrophilic C in the polar carbonyl group of the ketone. Electrons from the C=O move to the electronegative O creating an intermediate metal alkoxide complex.
Step 4:
This is the  work-up step, a simple acid/base reaction. Protonationof the alkoxide oxygen creates the alcohol product from the intermediate complex. 

 


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© Dr. Ian Hunt, Department of Chemistry, University of Calgary