Question 16

For (P): Cyclohexene $\xrightarrow{O_3, Zn}$ Hexanedial $\xrightarrow{NaOH, \Delta}$ Cyclopent-1-ene-1-carbaldehyde. Protecting the aldehyde as an acetal followed by hydroboration-oxidation adds an $-OH$ group at the $\beta$-carbon (C2) and $-H$ at the $\alpha$-carbon (C1) relative to the protected group. Acidic hydrolysis restores the aldehyde, which is reduced by $NaBH_4$ to a primary alcohol, yielding 2-(hydroxymethyl)cyclopentan-1-ol (Structure 3).

For (Q): 1-Methylcyclohex-1-ene $\xrightarrow{O_3, Zn}$ 6-Oxoheptanal. Intramolecular aldol condensation (with the aldehyde as the preferred electrophile) gives 1-acetylcyclopent-1-ene. Protecting the ketone as a ketal, followed by hydroboration-oxidation, adds $-OH$ at C2. Deprotection and subsequent $NaBH_4$ reduction of the ketone gives 1-(1-hydroxyethyl)cyclopentan-2-ol (Structure 5).

For (R): 2-Methylcyclopent-2-en-1-one is first protected as a ketal. Oxymercuration-demercuration (Markovnikov addition) adds $-OH$ at the more substituted C2 position. Deprotection followed by reduction of the C1 ketone gives 2-methylcyclopentane-1,2-diol (Structure 4).

For (S): 2-Methylcyclopent-2-en-1-one is protected. Hydroboration-oxidation (anti-Markovnikov addition) adds $-OH$ at the less substituted C3 position. Deprotection followed by reduction of the C1 ketone gives 2-methylcyclopentane-1,3-diol (Structure 1).

Thus, the correct match is P-3, Q-5, R-4, S-1. Correct Option: (A)