Question

Show reaction sequences that explain these transformations:

Short answer

It is the reaction of the enolate ion with another carbonyl group that leads to the form of $\mathbf{\alpha }\mathbf{,}\mathbf{\beta }$unsaturated aldehyde or ketone.

Step-by-step solution

Aldol self-condensation

It is the reaction of the enolate ion with another carbonyl group that leads to the form of $\mathbf{\alpha }\mathbf{,}\mathbf{\beta }$unsaturated aldehyde or ketone.

Michael Reaction

It is the 1,2addition or 1,4addition reaction of the Michael donor which is resonance stabilized carbanion to the Michael acceptor which is a carbonyl compound.

 Aldol cyclisation

It is the nucleophilic acyl substitution reaction of the carbonyl group forming the enolate ion which leads to the cyclisation with the carbonyl group in the molecule which leads to the formation of $\mathbf{\alpha }\mathbf{,}\mathbf{\beta }$unsaturated ketone or aldehyde.

 Decarboxylation

It is the reaction which leads to the removal of the carbonyl group and the release of carbon di-oxide $\left({\mathrm{CO}}_2\right)$. Decarboxylation occurs by providing heat in the reaction.

Mechanism for compound A

1. Acidic hydrogen protonated
2. Formation of the enolate ion
3. Aldol condensation
4. Michael’s reaction
5. Aldol cyclisation
6. Decarboxylation

Mechanism of reaction

Mechanism for compound B

1. Acidic hydrogen protonated
2. Formation of enolate ion
3. Claisen condensation
4. Michael reaction
5. Decarboxylation

Michael followed by Claisen condensation: hydrolysis and decarboxylation