Bondline / Reactions

Claisen condensation

An ester enolate attacks a second ester; the tetrahedral intermediate expels alkoxide to give a β-keto ester. Deprotonation of the acidic product drives the reaction.

Enolates · 3 steps

Conditions

NaOR matching the ester’s alkoxy group (e.g. NaOMe for methyl esters), then acid workup.

Mechanism in 3 steps

Red curly arrows show where each pair of electrons moves.

O−HOOOO−OO++
Step 1Methoxide removes an α-proton, giving the ester enolate.
OO−OOOOOO−+
Step 2The enolate attacks the carbonyl carbon of a second ester molecule.
OOOO−OOOO−+
Step 3The tetrahedral intermediate collapses and expels methoxide.

About enolates reactions

A C–H next to a carbonyl is acidic, because the anion formed (an enolate) is stabilised by resonance. Enolates are carbon nucleophiles that make new C–C bonds.

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