Q19 · CSIR-NET Chemistry, June 2013
Paper: CSIR-NET June 2013 · Subject: Organic Chemistry · Chapter: Reagents, Reaction Mechanisms & Named Reactions · Topic: Named Reactions · Marks: 2 · Difficulty: Medium
The major product formed in the following reaction is: 
(a)
(b)
(c)
(d)
Answer
Answer: B ✓ checked by 4AB · confidence medium
Explanation
Ueno–Stork: the bromoacetal radical cyclises 5-exo onto the vinyl group; Jones reagent then oxidises the acetal to the γ-lactone. A 4-substituent (t-Bu) directs the new ring methyl trans to itself (Beckwith), so the 4-methyl-5-t-butyl lactone is trans (b).
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