ALPHA CARBON REACTIONS

Introduction

This page focuses on reactions that deal with the alpha carbon in carbonyl-containing compounds.

Reactions

Acid-catalyzed ketone-enol tautomerization

Tautomerization reactions are part of other mechanisms and are shown here and not in other places for simplicity

Base-catalyzed ketone-enol tautomerization

α halogenation

These reactions works with chlorine, bromine, and iodine.

In acidic conditions

In basic conditions

Haloform reaction (also in basic conditions)

When performed with iodine, this reaction may be used as a test for a methyl ketone

Hell-Volhard-Zelinsky reaction

Aldol

If the reaction is performed with heat, elimination in an E1cb reaction can occur. If extensive conjugation results from E1cb, heat may not be needed.

Elimination under basic conditions

Elimination under acidic conditions

Claisen condensation

Intramolecular Claisen condensation (Dieckmann cyclization)

Alkylation of the α proton

Use LDA at -78˚C to alkylate the less substituted side. Use a nonsterically hindered base like NaH to alkylate the more substituted side

Malonic ester synthesis

Acetoacetic ester synthesis

Michael addition

Stork enamine synthesis

Click here for the mechanism of enamine formation.