Q21 · CSIR NET Chemistry, December 2016
Paper: CSIR NET December 2016 · Subject: Organic Chemistry · Chapter: Reagents, Reaction Mechanisms & Named Reactions · Topic: Named Reactions · Marks: 2 · Difficulty: Medium
The correct starting compound A in the following reaction is (A) 
cat. $\mathrm{CH_3CH_2CO_2H}$, heat 
cat. $\mathrm{CH_3CH_2CO_2H}$, heat (a)
(b)
(c)
(d)
Answer
Answer: B ✓ checked by 4AB · confidence medium
The source book printed A; on checking, B is correct — see the explanation.
Explanation
Johnson–Claisen: the secondary allylic alcohol (b) forms the ketene acetal with triethyl orthoacetate and the chair [3,3] shift moves the C=C next to the CH₂OBn and forms the new C–C bond at the methyl-bearing carbon, on the face the C–O bond occupied — the product shown.
Study loop for Reagents, Reaction Mechanisms & Named Reactions