See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the transformation: The starting material is cyclohexane-1,2,4-triol (three OH groups on a cyclohexane ring). The product is 4-oxocyclohexane-1,2-diol (the OH at C4 is oxidized to a ketone, while the vicinal diol at C1,C2 is preserved). Step 2 - Strategy: We need to selectively oxidize the single secondary alcohol at C4 while leaving the vicinal diol (C1,C2) untouched. The approach is: (i) Protect the vicinal diol (C1,C2) as an acetonide (cyclic ketal) using Me2CO/H+. This selectively protects the cis-1,2-diol as it can form a five-membered cyclic ketal, leaving the C4-OH free. (ii) Oxidize the free C4-OH to a ketone using KMnO4 (used as an oxidant for secondary alcohols under appropriate conditions). (iii) Remove the acetonide protecting group by acid hydrolysis with H3O+ to regenerate the free 1,2-diol. Step 3 - Match to options: Option (b) Me2CO/H+, KMnO4, H3O+ follows exactly this sequence: protect the diol as acetonide, oxidize the free alcohol with KMnO4, then deprotect with aqueous acid. Step 4 - Why other options fail: (a) Uses KMnO4/HO- as the last step, which would cause over-oxidation or open the diol under basic conditions; also the order is wrong. (c) KMnO4/NaO4 is not a standard reagent combination for selective alcohol oxidation; NaIO4 is used with OsO4 for diol cleavage, not here. (d) KMnO4/NaIO4 at the start would cleave the vicinal diol (periodate cleaves 1,2-diols), destroying the desired diol before protection. Step 5 - Conclusion: Option (b) is the only sequence that correctly protects the 1,2-diol first, selectively oxidizes C4-OH, and then deprotects. Therefore, the correct answer is B.