Chapter 21, Problem 21.28P

Interpretation Introduction

Interpretation:

The complete, detailed mechanism for the given reaction is to be drawn, and major product for the same reaction is to be predicted.

Concept introduction:

The intramolecular Claisen condensation of the diester, on treatment with a strong base, leads to form the $\text{β-keto}$ ester. This is known as the Dieckmann condensation reaction. the α carbon of the carbonyl compound has an acidic proton, which can be easily abstracted by the strong base. The carbanion is formed, which is resonance stabilized with corresponding more stable enolate form. This enolate adds the second carbonyl carbon of the diester, and simultaneously, the alkoxide group (${\text{RO}}^{\text{-}}$) is eliminated to form the $\text{β-keto}$ ester as the product. So the Dieckmann condensation involves intramolecular nucleophilic addition-elimination reaction. In most of the cyclization reaction, Dieckmann condensation occurs. Dieckmann condensation does not occur when the ring size is less than five-member or more than eight members due to angle strain. The proton of α carbon of the ketones and aldehydes is more acidic than that of ester.