91Ó°ÊÓ

When two molecules of ester get subjected to a condensation reaction, it is termed Claisen condensation. The product generated in this reaction is a ß -keto ester.

This reaction is reversible and favors the reactant side as it is more stable than the ß -keto ester.

a. The first reaction is an intermolecular Claisen condensation. An intramolecular condensation reaction forms the final product. The reaction is given below.

Reaction (a)

b. This reaction involved two successive aldol condensation reactions. In this reaction, phthalaldehyde reacts with cyclohexane-1,4-dione in the presence of ^-OH to form (E)-2-((2,5-dioxocyclohexylidene)methyl)benzaldehyde.

This further reacts with ^-OH to form 2,3-dihydroanthracene-1,4-dione. The reaction can is given below.

Reaction (b)

c. In this reaction, the base removes a proton from the carbon flanked by two carbonyl groups. This is followed by an intramolecular S_N2 reaction. In this reaction, (S)-6-bromocyclononane-1,3-dione reacts with ^-OH and the proton gets abstracted from the carbon flanked by two carbonyl groups.

This further leads to the formation of a six-membered ring fused with a five-membered ring having a carbonyl group.

The reaction is given below.

Reaction (c)

d. A proton is removed from the α -carbon flanked by a carbonyl group and nitrile. This further leads to an intramolecular S_N2 reaction occurs. The reaction is given below.

Reaction (d)