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JEE Advanced levelSingle correct optionDifficulty 3 of 3o3204

Benzyne is generated in the presence of 2-methylfuran and trapped by a [4+2] cycloaddition across C-2 and C-5 of the furan. How does the adduct exist?

  1. AAs a single achiral compound with a mirror plane
  2. BAs four stereoisomers because there are two stereocentres
  3. CAs a racemic mixture of two enantiomers (the bridged ring allows only one relative configuration of the two bridgehead stereocentres)
  4. DAs two diastereomers in a ratio set by the methyl group

Answer: C

The product is 1-methyl-1,4-dihydro-1,4-epoxynaphthalene. The methyl group is on only one bridgehead carbon, so no mirror plane exists and the molecule is chiral. The oxygen bridge forces the two bridgehead carbons into one relative configuration, so only a pair of enantiomers is possible. Benzyne attacks both faces of the planar furan equally, giving a racemate.
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