Q19 · CSIR-NET Chemistry, December 2016
Paper: CSIR-NET December 2016 · Subject: Organic Chemistry · Chapter: Reagents, Reaction Mechanisms & Named Reactions · Topic: Reduction Reagents · Marks: 2 · Difficulty: Medium
Under review — part of this question (a structure or an option) is not clear in the source scan. 4AB is checking it against the original book; the answer shown may change.
The correct sequence of reagents for the following conversion is: 
(a)i) $\mathrm{K}_{2} \mathrm{CO}_{3}$, ii) $\mathrm{CHCCOCH}_{3}$, iii) $\mathrm{Br}_{2}$, iv) $\mathrm{NaBH}_{4}$
(b)i) $\mathrm{NaBH}_{4}$, ii) $\mathrm{CHCCOCH}_{3}$, iii) $\mathrm{Br}_{2}$, iv) $\mathrm{K}_{2} \mathrm{CO}_{3}$
(c)i) $\mathrm{CHCCOCH}_{3}$, ii) $\mathrm{NaBH}_{4}$, iii) $\mathrm{Br}_{2}$, iv) $\mathrm{K}_{2} \mathrm{CO}_{3}$
(d)i) $\mathrm{Br}_{2}$, ii) $\mathrm{CHCCOCH}_{3}$, iii) $\mathrm{K}_{2} \mathrm{CO}_{3}$ iv) $\mathrm{NaBH}_{4}$
Answer
Under review — not yet confirmed.
Answer: A
Explanation
K₂CO₃ generates bromonitrile oxide, which undergoes [3+2] cycloaddition with but-3-yn-2-one to give the 3-bromo-5-acetylisoxazole. Br₂ α-brominates the methyl ketone and NaBH₄ reduces it to the bromohydrin (a).
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