Mechanism of Condensation Reaction Claisen Condensation Reaction

MECHANISM OF THE CLAISEN CONDENSATION
Step 1: First, an acid-base reaction. The alkoxide functions as a base and removes the acidic a-hydrogen giving the reactive ester enolate.
Step 2: The nucleophilic ester enolate attacks the carbonyl C of another ester in a nucleophilic substitution processgiving the tetrahedral intermediate.
Step 3: The intermediate collapses, reforming the C=O, resulting in loss of the leaving group, the alkoxide, leading to the b-ketoester product.
The Claisen condensation is an organic reaction used to form a carbon-carbon bond between two ester molecules using an alkoxide base in alcohol to make a β-keto ester. The R group of the ester starting material, the alkoxide base, and the alcohol solvent are chosen to be the same to not end up with a mixture of products. The ester starting material must have an α-hydrogen which is abstracted by the base to form an enolate and alcohol. The enolate then attacks the carbonyl carbon of another ester molecule, an OR group is released to regenerate the base, and the final β-keto ester product is formed. The intramolecular form of the Claisen condensation is the Dieckmann condensation. The Claisen condensation is the ester analogue of the Aldol condensation. Reagents : most commonly the base would be the alkoxide, R'O- The reaction involves an ester enolate reacting with another molecule of the ester. Remember enolates are good nucleophiles and the ester carbonyl C are electrophilic. The products of these reactions are β-ketoesters which are important, useful synthetic intermediates. Note that the product is the original ester with an acyl group added i.e. an acylation reaction has occurred. A simple example of a Claisen condensation is the reaction of ethyl ethanoate which is shown below in two representations.