The List-I contains products obtained from the reaction of compounds in List-I with \(\mathrm{O_3/Zn-H_2O}\) followed by cyclization (via more stable enolate) in the presence of aqueous \(\mathrm{NaOH}\). Match each entry in List-I with appropriate entry in List-II and choose the correct option.
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Important reactions involved:
• Ozonolysis:
\[
\mathrm{C=C \xrightarrow[Zn/H_2O]{O_3} Carbonyl\ compounds}
\]
• Intramolecular aldol reaction:
Enolate attacks intramolecular carbonyl center to form cyclic \(\beta\)-hydroxy carbonyl compounds.
• More substituted enolates are generally more stable and dominate under thermodynamic conditions.
In cyclic systems, always analyze:
• ring strain
• favored ring size
• stability of enolate intermediate
before predicting the major cyclized product.
\(P \rightarrow 2;\ Q \rightarrow 4;\ R \rightarrow 1;\ S \rightarrow 3\)
\(P \rightarrow 3;\ Q \rightarrow 4;\ R \rightarrow 5;\ S \rightarrow 2\)
\(P \rightarrow 2;\ Q \rightarrow 1;\ R \rightarrow 5;\ S \rightarrow 3\)
\(P \rightarrow 3;\ Q \rightarrow 5;\ R \rightarrow 4;\ S \rightarrow 2\)
Show Solution
The Correct Option isB
Solution and Explanation
Step 1: Understanding the Concept:
This problem sequence involves:
1. Ozonolysis (\(O_3/Zn, H_2O\)): Cleavage of the alkene double bond to form two carbonyl groups (dicarbonyl compound).
2. Intramolecular Aldol Condensation: In the presence of \(NaOH\), one carbonyl forms an enolate which attacks the other carbonyl to form a cyclic \(\alpha,\beta\)-unsaturated ketone. The "more stable enolate" rule means forming a 5 or 6 membered ring is preferred over others. Step 3: Detailed Explanation: (P) A bicyclic system with a central double bond.
Ozonolysis opens the central ring to form a large dicarbonyl ring with side chains. Cyclization reforms a bicyclic system.
Match: P \(\rightarrow\) 2. (Q) A 7-membered ring fused to a 5-membered ring with a double bond at the junction.
Ozonolysis yields a diketone. Intramolecular aldol condensation typically favors forming a 6-membered ring over a 5-membered one if possible.
Match: Q \(\rightarrow\) 1. (R) Two 6-membered rings fused with a double bond.
Following the same logic of ring opening and re-closing to the most stable size.
Match: R \(\rightarrow\) 5. (S) Another fused system.
Match: S \(\rightarrow\) 3. Step 4: Final Answer:
The complex set of ozonolysis followed by aldol cyclization leads to specific bridged or fused products depending on the initial chain length between carbonyls. Option (C) provides the correct mapping.
