Chapter 18: Enols and Enolates

Summary

• Enolates are good nucleophiles and reaction with alkyl halides via S_N2 type reactions.
• This allows alkyl groups to be introduced in the α-positions.
• Since the reaction is an S_N2 reaction, methyl and primary halides are most suitable for alkylation reactions.
• There can be problems due to competing condensation reactions.
• Methods to avoid this problem are discussed in Chapter 21

• Other substitution reactions of alkyl halides
• Alkylation of Ester Enolates

MECHANISM OF ALKYLATION OF ALDEHYDES AND KETONES
Step 1: First, an acid-base reaction. Hydroxide functions as a base and removes the acidic α-hydrogen giving the reactive enolate.
Step 2: The nucleophilic enolate attacks the alkyl halide at the electrophilic carbon carrying the halogen via an SN2 type process giving alkylated ketone and a bromide ion.

© Dr. Ian Hunt, Department of Chemistry