Q17 · CSIR NET Chemistry, June 2015
Paper: CSIR NET June 2015 · Subject: Organic Chemistry · Chapter: Reagents, Reaction Mechanisms & Named Reactions · Topic: Reagents, Reaction Mechanisms & Named Reactions – General · Marks: 2 · Difficulty: Medium
The products A and B in the following reaction sequence are 18-crown-6, rt. $\mathrm{A}$ $\mathrm{B}$
(a)$\mathrm{A}=$ 
$\mathrm{B}=$ 
$\mathrm{B}=$ (b)$\mathrm{A}=$ 
$\mathrm{B}=$ 
$\mathrm{B}=$ (c)$\mathrm{A}=$ 
$\mathrm{B}=$ 
$\mathrm{B}=$ (d)$\mathrm{A}=$ 
$\mathrm{B}=$ 
$\mathrm{B}=$ Answer
Answer: B ✓ checked by 4AB · confidence medium
Explanation
KH/18-crown-6 triggers an anionic oxy-Cope through a chair TS, giving the δ,ε-unsaturated aldehyde A with the two methyls syn. The non-stabilised ylide gives the Z-alkene in B (b).
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