Conjugate Addition

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Conjugate Addition
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Conjugate Addition

• Remember from Chapter 16 nucleophiles react
  with the carbonyl carbon of aldehydes or ketones.
  This process is nucleophilic addition.
• Nucleophiles can react with a,b-unsaturated
  aldehydes and ketones.
• The reaction takes place at the b-carbon.
• This process is known as conjugate addition.

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Conjugate Addition Step One
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Conjugate Addition Step Two
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Conjugate Addition

• Conjugate addition works because resonance of the
  unsaturated aldehyde or ketone places positive
  charge on the b-carbon.
• Resonance thus makes the b-carbon a good site for
  attack by nucleophiles (electron-pair donors).

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Resonance in a,b-Unsaturated Aldehydes and Ketones
Note the presence of positive charge on the
b-carbon
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Example
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Example
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Michael Addition

• We can now combine our understanding about the
  nucleophilic properties of enolate ions with our
  understanding of the mechanism of conjugate
  addtions.
• This brings about a new reaction, the Michael
  Addition Reaction.

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Michael Addition
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Mechanism First Step
Note the position of the equilibrium
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Mechanism Second Step
Conjugate addition
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Mechanism Third Step
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Michael Addition

• The acceptor in the Michael Addition Reaction can
  be any a,b-unsaturated aldehyde, ketone, ester,
  nitrile or nitro compound.
• The donor can be a b-diketone, a
  b-ketoester, a malonic ester, a b-ketonitrile, or
  a nitro compound.
• Clearly, the Michael Addition reaction represents
  an important means of synthesizing a wide variety
  of substances!