JEE Advanced 2024 Paper 1 · Q16 · Multistep Synthesis (Ozonolysis / Hydroboration / Acetal)
$\mathbf{List\text{-}I}$ contains various reaction sequences and $\mathbf{List\text{-}II}$ contains the possible products. Match each entry in $\mathbf{List\text{-}I}$ with the appropriate entry in $\mathbf{List\text{-}II}$ and choose the correct option.
$\mathbf{List\text{-}I}$ (substrate + reagents in given order): (P) Cyclohexene with reagents — i) $O_3$, Zn ii) aq. NaOH, $\Delta$ iii) ethylene glycol, PTSA iv) a) $BH_3$, b) $H_2O_2$, NaOH v) $H_3O^+$ vi) $NaBH_4$ (Q) 1-Methylcyclohex-1-ene with reagents — i) $O_3$, Zn ii) aq. NaOH, $\Delta$ iii) ethylene glycol, PTSA iv) a) $BH_3$, b) $H_2O_2$, NaOH v) $H_3O^+$ vi) $NaBH_4$ (R) Cyclopent-2-en-1-one substrate (figure) — i) ethylene glycol, PTSA ii) a) $Hg(OAc)_2$, $H_2O$, b) $NaBH_4$ iii) $H_3O^+$ iv) $NaBH_4$ (S) 2-Methylcyclopent-2-en-1-one substrate (figure) — i) ethylene glycol, PTSA ii) a) $BH_3$, b) $H_2O_2$, NaOH iii) $H_3O^+$ iv) $NaBH_4$
$\mathbf{List\text{-}II}$ (cyclopentane products): (1) cyclopentane diol structure 1; (2) hydroxymethylcyclopentanol structure 2; (3) trans-2-methylcyclopentane-1,3-diol; (4) cyclopent-1-ene-cis-diol; (5) 2,2-dimethylcyclopentane-1,3-diol structure (figure).
Reveal answer + step-by-step solution
Correct answer:A
Solution
(P) Cyclohexene → ozonolysis (Zn) gives hexanedial OHC(CH2)4CHO → intramolecular aldol (NaOH/Δ) → cyclopent-1-ene-1-carbaldehyde → ethylene glycol/PTSA protects -CHO as cyclic acetal → BH3/H2O2/NaOH (anti-Markovnikov hydration of C=C) gives -CH2OH on cyclopentane ring → H3O+ deprotects acetal → NaBH4 reduces -CHO to -CH2OH. Final = trans-2-(hydroxymethyl)cyclopentan-1-ol type → matches (3). (Q) 1-methyl-cyclohexene → ozonolysis gives a 6-carbon keto-aldehyde with a methyl branch → intramolecular aldol → methyl-substituted cyclopentenone-type aldehyde; after acetal protection, hydroboration-oxidation places OH at the less-substituted position; deprotection then NaBH4 reduces ketone/aldehyde → 2-methyl substituted diol corresponding to (5). (R) Cyclopent-2-en-1-one → acetal-protect ketone → oxymercuration-demercuration of C=C (Markovnikov hydration) → deprotect → reduce remaining C=O → cis-1,3-diol on cyclopentane = (4). (S) 2-Methylcyclopent-2-en-1-one → protect ketone → BH3/H2O2 (anti-Mark.) gives OH on C3 → deprotect → NaBH4 → 2,2-dimethyl-substituted-style 1,3-diol pattern → (1). Mapping P-3, Q-5, R-4, S-1 = option (A).
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