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

Reduction of Amides
(for more detail see Chapter 22)

reduction of amides using LiAlH4
Reactions usually in Et2O or THF followed by H3O+ work-ups

Reaction type:  Nucleophilic Acyl Substitution then Nucleophilic Addition

Summary

hydride reductions of different types of amides
MECHANISM OF THE REACTION OF LiAlH4 WITH AN AMIDE
Step 1:
The nucleophilic H from the hydride reagent adds to the electrophilic C in the polar carbonyl group of the ester. Electrons from the C=O move to the electronegative O creating the tetrahedral intermediate, a metal alkoxide complex.
reduction of an amide using hydride
Step 2:
The tetrahedral intermediate collapses and displaces the O as part of a metal alkoxide leaving group, this produces a highly reactive iminium ion an intermediate.
Step 3: 
Rapid reduction by the nucleophilic H from the hydride reagent as it adds to the electrophilic C in the iminium system. π electrons from the C=N move to the cationic N neutralising the charge creating the amine product.
 

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