Q33 · CSIR NET Chemistry, December 2019
Paper: CSIR NET December 2019 · Subject: Organic Chemistry · Chapter: Reagents, Reaction Mechanisms & Named Reactions · Topic: Named Reactions · Marks: 2 · Difficulty: Medium
The structure of A in the following reaction is 
\[ \mathrm{A}\ \xrightarrow[\text{2. NaOEt, EtOH}]{\substack{\text{1. i) }h\nu\\ \text{ii) }\mathrm{O_3,\ Me_2S}}} \]
(b)
(c)
(d)
(a)
Answer
Answer: A ✓ checked by 4AB · confidence medium
Explanation
But-2-ynyl acrylate (a) undergoes intramolecular [2+2] photocycloaddition between the alkyne and the acrylate to give a cyclobutene-fused lactone; ozonolysis cleaves the cyclobutene to a 1,4-diketone and NaOEt aldol condensation closes the cyclopentenone — the bicyclic enone lactone shown, which carries no methyl.
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