Q23 · CSIR NET Chemistry, December 2015
Paper: CSIR NET December 2015 · Subject: Organic Chemistry · Chapter: Reagents, Reaction Mechanisms & Named Reactions · Topic: Reagents, Reaction Mechanisms & Named Reactions – General · Marks: 2 · Difficulty: Medium
The major structures of A and B in the following reaction sequence are 
$\text{A}\ \xrightarrow[\text{t-BuOH, heat}]{\text{t-BuOK diglyme}}\ \text{B}$
$\text{A}\ \xrightarrow[\text{t-BuOH, heat}]{\text{t-BuOK diglyme}}\ \text{B}$(a)A = 
B = 
B = (b)A = 
B = 
B = (c)A = 
B = 
B = (d)A = 
B = 
B = Answer
Answer: B ✓ checked by 4AB · confidence medium
Explanation
Semicarbazide condenses with the enone C=O through its terminal hydrazinic NH₂. This gives the semicarbazone R₂C=N–NH–CO–NH₂ (A as drawn in (b); option (a) shows the wrong connectivity, H₂N–NH–CO–N=). Heating with t-BuOK in diglyme/t-BuOH is a Wolff–Kishner reduction, which turns the C=N carbon into CH₂ and gives the octalin B. B is drawn the same in (a) and (b), so the A structure decides the answer: (b).
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