Question

Match the major products obtained in the reactions given in List-I with the corresponding structures in List-II and choose the correct option.

• A. \(P \rightarrow 2;\ Q \rightarrow 1;\ R \rightarrow 5;\ S \rightarrow 4\)
• B. \(P \rightarrow 1;\ Q \rightarrow 2;\ R \rightarrow 4;\ S \rightarrow 5\)
• C. \(P \rightarrow 1;\ Q \rightarrow 2;\ R \rightarrow 3;\ S \rightarrow 4\)
• D. \(P \rightarrow 2;\ Q \rightarrow 1;\ R \rightarrow 3;\ S \rightarrow 5\)

Hint:

Important transformations to remember:
• Hydroximoyl halides in base form nitrile oxides.
• Nitrile oxides may undergo:
• cyclization
• hydrolysis
• rearrangement
• Oxime derivatives often undergo:
• Beckmann rearrangement
• heterocyclic ring formation Always identify:
• reactive intermediate
• neighboring nucleophile
• possibility of intramolecular cyclization before predicting the final product.

Answer 1

The Correct Option is A

Concept: This problem involves reactions of:
• hydroximoyl halides
• oxime derivatives
• nitrile oxide intermediates
• cyclization reactions
• Beckmann-type rearrangements The key strategy is to identify the reactive intermediate formed in each reaction condition and then determine the most stable product obtained.

Step 1: Analyzing reaction \(P\). The substrate in \(P\) is a hydroximoyl bromide: \[ \mathrm{Ar-CH=C(Br)-N-OH} \] Treatment with aqueous \(\mathrm{NaOH}\) causes dehydrohalogenation. This generates a nitrile oxide intermediate: \[ \mathrm{Ar-C \equiv N^+-O^-} \] Under aqueous basic conditions, nitrile oxides undergo hydrolysis producing hydroxy nitrile derivatives. The final product corresponds to structure \((2)\). Hence: \[ P \rightarrow 2 \]

Step 2: Analyzing reaction \(Q\). Reagents used: \[ 1.\ (\mathrm{CH_3CO})_2\mathrm{O} \qquad 2.\ \mathrm{Na_2CO_3} \] Acetic anhydride first acetylates the oxime hydroxyl group. The activated intermediate then undergoes rearrangement and elimination. Finally cyanophenol derivative is formed. The resulting structure matches compound \((1)\). Therefore: \[ Q \rightarrow 1 \]

Step 3: Analyzing reaction \(R\). Here the substrate contains a methyl-substituted hydroximoyl bromide. On treatment with aqueous \(\mathrm{NaOH}\), intramolecular cyclization occurs via nitrile oxide intermediate formation. This leads to formation of benzisoxazole derivative. The obtained product corresponds to structure \((5)\). Thus: \[ R \rightarrow 5 \]

Step 4: Analyzing reaction \(S\). In \(S\), the substrate is an acetylated oxime derivative. Treatment with aqueous \(\mathrm{Na_2CO_3}\) promotes cyclization. Intramolecular nucleophilic attack followed by ring closure produces benzisoxazole derivative. The structure formed corresponds to compound \((4)\). Therefore: \[ S \rightarrow 4 \]

Step 5: Final matching. Thus the correct matching is: \[ P \rightarrow 2 \] \[ Q \rightarrow 1 \] \[ R \rightarrow 5 \] \[ S \rightarrow 4 \] This corresponds to option (A). Final Answer: \[ \boxed{(A)} \]