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JEE Advanced levelSingle correct optionDifficulty 3 of 3co093

Ethyl 3-oxobutanoate (1 mol) reacts with but-3-en-2-one in the presence of NaOEt. The Michael adduct then undergoes an intramolecular aldol condensation with loss of water, with the ester group retained. The final product is

  1. Aethyl 4-methyl-2-oxocyclohex-3-ene-1-carboxylate
  2. Bethyl 2-methyl-4-oxocyclohex-2-ene-1-carboxylate
  3. Cethyl 2-methyl-4-oxocyclopent-2-ene-1-carboxylate
  4. Dethyl 3-methyl-5-oxocyclohex-3-ene-1-carboxylate

Answer: B

Michael addition gives . The terminal methyl of the butanone chain forms an enolate and attacks the acetyl C=O, closing a six-membered ring. Dehydration gives the conjugated enone, in which the ring carbon bearing is next to the carbon bearing the methyl group (Hagemann's ester).
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