See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Concept: The transformation requires converting a ketone group (C=O) in the side chain -CH2-C(=O)-CH3 to a methylene group (-CH2-), i.e., complete deoxygenation of the carbonyl to give -CH2-CH2-CH3. This is a C=O → CH2 reduction. Step 1 – Identify what needs to be done: The starting material has a ketone (methyl ketone, -COCH3) in the side chain. The product has a propyl group (-CH2CH2CH3), meaning the C=O has been fully reduced to CH2 (deoxygenation, not just reduction to alcohol). Step 2 – Identify which reagents achieve C=O → CH2: - Clemmensen reduction (Zn(Hg)/HCl) reduces C=O → CH2 under acidic conditions. - Wolff-Kishner reduction (NH2NH2/KOH/heat) reduces C=O → CH2 under basic conditions. - LiAlH4 reduces C=O → CHOH (alcohol), not full deoxygenation. - NaBH4 reduces C=O → CHOH (alcohol), not full deoxygenation. Step 3 – Consider compatibility with the acetal group: - The molecule contains a cyclic acetal (1,3-dioxolane). Acetals are stable under basic conditions but hydrolyze under acidic conditions. - Clemmensen reduction uses strongly acidic conditions (HCl), which would hydrolyze the acetal, destroying the protecting group. Therefore Clemmensen reduction is NOT suitable. - Wolff-Kishner reduction uses strongly basic conditions (KOH/hydrazine/heat), under which acetals are stable. The acetal survives, and the ketone is fully deoxygenated to give the propyl group. Step 4 – Eliminate options: - (a) Clemmensen: would hydrolyze the acetal under acidic conditions — incompatible. - (c) LiAlH4: only reduces to alcohol, not full deoxygenation. - (d) NaBH4: only reduces to alcohol, not full deoxygenation. - (b) Wolff-Kishner: achieves C=O → CH2 under basic conditions, acetal is stable → correct. Therefore, the correct answer is B.