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Question #44003

Difficulty: 8/10 | 🟢 Free

The Question

Consider the reaction of ethyl 2-oxocyclopentane-1-carboxylate with the following sequence of reagents:

$\ce{C6H5MgBr}$ (1 equivalent), dry THF, $298\text{ K}$
$\ce{CH2=CH-CH2Br}$ (1 equivalent), $298\text{ K}$
Mild $\ce{H3O+}$

Identify the major organic product formed.

Options

A.
Ethyl 1-allyl-2-oxocyclopentane-1-carboxylate
B.
Ethyl 2-(allyloxy)-2-phenylcyclopentane-1-carboxylate
C.
Ethyl 2-hydroxy-2-phenylcyclopentane-1-carboxylate
D.
Ethyl 2-(allyloxy)cyclopent-1-ene-1-carboxylate

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.

Concepts Behind This Question

Grignard Reaction Pathways|Inductive Effect Trends|Basicity-Solvation Competition

Why This Question Is Tricky

Common Mistakes

The problem tests the critical competition between the nucleophilicity and basicity of Grignard reagents.

Students often mechanically add Grignard reagents to the most electrophilic carbonyl (the ketone), leading to incorrect addition products (Options B and C).

However, the presence of a highly acidic $\alpha$ -proton in the $\beta$ -keto ester acts as a 'Hidden Variable'.

The Grignard reagent acts exclusively as a strong base, forming an enolate and neutralizing its nucleophilic potential.

Furthermore, the problem tests the regioselectivity of the resulting magnesium enolate, which preferentially undergoes C-alkylation rather than O-alkylation (Option D) upon treatment with an alkyl halide due to the tight, covalent nature of the magnesium-oxygen bond.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Aldehydes, Ketones, and Carboxylic Acids - Class 12
Concept	Grignard Reaction Pathways
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free