See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Concept: The transformation requires reduction of a ketone (C=O) to a methylene group (CH2). This is a deoxygenation, not a simple reduction to an alcohol. There are two classical methods for this: the Clemmensen reduction (Zn(Hg)/HCl) and the Wolff-Kishner reduction (NH2NH2/KOH/heat). The key constraint here is that the starting material contains a 1,3-oxathiolane ring (a mixed O,S-acetal), which is acid-sensitive. Under strongly acidic conditions (Zn(Hg)/HCl — Clemmensen), the acid-labile O,S-acetal (oxathiolane) would be hydrolyzed/cleaved, destroying the ring system. Therefore, Clemmensen reduction (option a) is not suitable. Step-by-step reasoning: 1. The starting material has a ketone on the six-membered ring and a 1,3-oxathiolane (mixed acetal with O and S) at the spiro carbon. 2. The product retains the intact spiro ring system (oxathiolane ring preserved) but the ketone is converted to CH2. 3. Wolff-Kishner reduction (NH2NH2/KOH/Delta, option b) is carried out under strongly basic conditions. The oxathiolane ring is stable to basic conditions, so it survives. The ketone is converted to the hydrazone intermediate and then reduced to CH2 under the basic/thermal conditions. 4. LiAlH4 (option c) would reduce the ketone only to an alcohol (C=O → CHOH), not to CH2. It does not achieve full deoxygenation. 5. H2/Ni (option d) would also at best reduce the ketone to an alcohol under normal conditions, and would not achieve deoxygenation to CH2. 6. Zn(Hg)/HCl (option a) would achieve deoxygenation but would simultaneously cleave the acid-sensitive oxathiolane ring. 7. Therefore, Wolff-Kishner reduction (option b) is the only reagent that both deoxygenates the ketone to CH2 and preserves the oxathiolane ring intact. Therefore, the correct answer is B.