|Chapter 20: Carboxylic Acid Derivatives. Nucleophilic Acyl Substitution|
Reactions of RLi and RMgX
(review of Chapter 14)
Reaction type: Nucleophilic Acyl Substitution then NucleophilicAddition
MECHANISM OF THE REACTION OF RMgX WITH AN ESTER
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.
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.
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.
This is the work-up step, a simple acid/base reaction. Protonationof the alkoxide oxygen creates the alcohol product from the intermediate complex.
|© Dr. Ian Hunt, Department of Chemistry|