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Diethyl glutarate (EtOOC-CH2-CH2-CH2-COOEt) is treated sequentially with: (i) sodium ethoxide, (ii) H3O+, and then heated (Dieckmann cyclization followed by hydrolysis and decarboxylation). Identify the final organic product.

1. cyclopentanone
2. 2-ethoxycarbonylcyclopentanone
3. cyclopent-2-en-1-one
4. 2,2-dimethylcyclopentanecarboxylic acid

Correct answer: cyclopentanone

Solution

The Dieckmann cyclization of diethyl glutarate proceeds via intramolecular Claisen condensation. The alpha carbon of one ester attacks the carbonyl of the other, forming a 5-membered ring beta-keto ester: ethyl 2-oxocyclopentane-1-carboxylate. Acid hydrolysis converts the ester to a carboxylic acid (2-oxocyclopentane-1-carboxylic acid), and heating causes decarboxylation (beta-keto acid loses CO2) to give cyclopentanone.

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