Aldol Addition and Condensations
1. The aldehyde or ketone is converted to its enolate by abstraction, which is the removal of a proton by a base.
2. The enolate, acting as a nucleophile, is added to the carbonyl group.3. A proton is abstracted by the alkoxide product in Step 2 from water to make the aldol.
Mechanism of Aldol Addition
Crossed and Intramolecular Aldol Addition
In a practical crossed aldol reaction, two different carbonyl compounds mix together, and only one can form an enolate, preventing self-condensation of the other compound.A directed aldol reaction is a reaction in which the enolate is prepared in the first step and the intended reactant is added in the second step to ensure the desired product. In a directed aldol addition, a strong base, such as lithium diisopropylamide (LDA), causes immediate formation of the enolate, and then the compound intended to react to the enolate adds, ensuring the desired product.