91Ó°ÊÓ

Carbonyl condensation reactions are a set of reactions that involve two carbonyl systems, one of which acts as a nucleophile. The necessary criteria for such reactions are that one of the carbonyl compounds should contain an $\mathit{Î\pm }$-hydrogen. The reactions mostly occur in presence of a base.

The carbonyl condensation reactions are listed below:

1. The aldol reaction
2. Crossed aldol reactions
3. Directed aldol reactions
4. Intramolecular aldolreactions
5. The Claisen reaction
6. The crossed Claisenreaction
7. The Dieckmann reaction
8. The Michael reaction
9. The Robinsonannulation

The carbonyl compound with$\mathit{Î\pm }$-hydrogen is treated with the base to form an enolate.

Formation of enolate

The enolate acts as the nucleophile and attacks the second carbonyl compound.

When the other carbonyl compound is $\mathrm{Î\pm },\mathrm{β}$-unsaturated, the attack of nucleophile occurs at the $\mathrm{β}$-carbon position.

When it is a simple carbonyl, attack takes place at the electrophilic carbonyl carbon center.

Final step is the protonation followed by dehydration in some cases.

Mechanism of carbonyl condensation

The given reactions are examples of carbonyl condensation reactions. Following the general mechanism, the products of the reactions are given below:

a.