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Question #43966

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The Question

Octane-2,7-dione undergoes an intramolecular aldol condensation in the presence of aqueous \ce{NaOH} upon heating to yield compound $\mathbf{P}$ as the major product. $\mathbf{P}$ is subjected to dihydroxylation using catalytic \ce{OsO4} and NMO to form a cis-diol $\mathbf{Q}$ . Reaction of $\mathbf{Q}$ with acetone in the presence of catalytic $p$ -toluenesulfonic acid yields compound $\mathbf{R}$ . Finally, $\mathbf{R}$ is treated with reagent $\mathbf{X}$ to produce compound $\mathbf{S}$ (3a-ethyl-2,2,6a-trimethyl-tetrahydro-4H-cyclopenta[d][1,3]dioxole) as the major product.

Which of the following correctly identifies the IUPAC name of $\mathbf{R}$ and the appropriate reagent $\mathbf{X}$ ?

Options

A.
$\mathbf{R}$ : 1-(2,2,6a-trimethyl-tetrahydro-4H-cyclopenta[d][1,3]dioxol-3a-yl)ethan-1-one ; $\mathbf{X}$ : \ce{NH2NH2}, \ce{KOH}, ethylene glycol, $\Delta$
B.
$\mathbf{R}$ : 1-(2,2,6a-trimethyl-tetrahydro-4H-cyclopenta[d][1,3]dioxol-3a-yl)ethan-1-one ; $\mathbf{X}$ : \ce{Zn(Hg)}, conc. \ce{HCl}, $\Delta$
C.
$\mathbf{R}$ : 1-(1,2-dihydroxy-2-methylcyclopentyl)ethan-1-one ; $\mathbf{X}$ : \ce{Zn(Hg)}, conc. \ce{HCl}, $\Delta$
D.
$\mathbf{R}$ : 1-(2,2-dimethyl-1,3-dioxaspiro[4.4]non-6-yl)ethan-1-one ; $\mathbf{X}$ : \ce{NH2NH2}, \ce{KOH}, ethylene glycol, $\Delta$

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Exception_Exposure

Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.

Concepts Behind This Question

Aldol Condensation Directionality|Clemmensen vs. Wolff-Kishner|Reduction Selectivity (Hydrides)

Why This Question Is Tricky

Common Mistakes

This problem tests the strategic choice of reduction conditions in the presence of acid-sensitive protecting groups.

Students often blindly apply the Clemmensen reduction to ketones without analyzing the rest of the molecule.

Here, the acetonide (cyclic acetal) formed in Step 3 is stable to base but rapidly hydrolyzes in acid.

Using Clemmensen conditions would destroy the acetonide and trigger a Pinacol rearrangement of the exposed diol.

Wolff-Kishner is the mandatory choice to maintain structural integrity.

Quick Facts About This Question

Question Information

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