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SolutionsConjugate (1,4) or Michael Addition

1. 1,2- or 1,4-addition?

Give the main product of the reaction of 2-cyclohexenone with: a) KCN and acetic acid; b) lithium dimethylcuprate and then H2O; c) methyllithium and then H2O; d) LiAlH4 and then H2O; e) H2, Pd/C.

  1. 3-Oxocyclohexanecarbonitrile (1,4-addition).
  2. 3-Methylcyclohexanone (1,4-addition).
  3. 1-Methylcyclohex-2-en-1-ol (1,2-addition).
  4. Cyclohex-2-en-1-ol (1,2-addition).
  5. Cyclohexanone: the C=C, more reactive than the C=O towards hydrogenation, is reduced.

NaBH4 and Grignard reagents are not regioselective with these substrates and give mixtures of the 1,2- and 1,4-products.

2. Choosing the reagent

Which reagent would you use to convert 3-penten-2-one into: a) 4-methyl-2-hexanone; b) 3-methyl-4-hexen-3-ol?

  1. Lithium diethylcuprate, (CH3CH2)2CuLi, which gives conjugate addition, followed by hydrolysis.
  2. Ethyllithium, which attacks the carbonyl directly (1,2-addition), followed by hydrolysis.

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