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JEE Main levelSingle correct optionDifficulty 2 of 3co082

Cyclohexanone is treated with but-3-en-2-one and base. The overall transformation (Robinson annulation) proceeds as

  1. AClaisen condensation followed by decarboxylation
  2. BCannizzaro reaction followed by esterification
  3. CReformatsky reaction followed by dehydration, forming a five-membered ring
  4. DMichael addition followed by intramolecular aldol condensation, forming a new fused six-membered cyclohexenone ring

Answer: D

The cyclohexanone enolate adds 1,4 to the enone (Michael step) and gives a 1,5-diketone. The methyl ketone enolate then attacks the ring C=O in an intramolecular aldol, and dehydration gives a fused cyclohexenone. Robinson annulation is thus Michael plus aldol condensation.
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