Question

Intramolecular Claisen condensation given by Diester is known as :
(A) Stobbe condensation
(B) Dieckmann Condensation
(C) Mannich reaction
(D) Reformatsky reaction

Answer 1

Hint: The Claisen condensation is a carbon–carbon bond forming reaction that occurs between two esters or one ester and another carbonyl compound in the presence of a strong base, resulting in a $\beta -ketoester$ or a $\beta -diketone$.

Complete step by step answer:
We will discuss each option to know which of them is the required reaction.
The Stobbe condensation is a modification specific for the diethyl ester of succinic acid requiring less strong bases. A reaction mechanism that explains the formation of both an ester group and a carboxylic acid group is centered on a lactone intermediate.
Dieckmann condensation is the intramolecular condensation reaction of diesters with a base to give beta-ketoesters. As the nucleophile is an ester, therefore it is also an intramolecular Claisen condensation of Diester. It is named after the German chemist Walter Dieckmann (1869–1925).
The Mannich reaction is an organic reaction which consists of an amino alkylation of an acidic proton placed next to a carbonyl functional group by formaldehyde and a primary or secondary amine or ammonia. The final product is a $\beta -\text{amino carbonyl}$ compound also known as a Mannich base.
Reformatsky reaction is defined as an organic reaction that is used to convert ketone or an aldehyde and $\alpha -haloester$ to a $\beta - hydroxysterol$ by using metallic zinc and acid workup. Here, inert solvent like diethyl ether or THF(tetrahydrofuran) is often used as a solvent for the reaction.
So, the correct answer is “Option B”.

Note: Deprotonation of an ester at the alpha-position generates an enolate ion which then undergoes a 5-exo-trig nucleophilic attack to give a cyclic enol. Protonation with a Bronsted-Lowry acid re-forms the $\beta -ketoester$.