1,4-addition of enolates to enones (“The Michael Reaction”)

by James

Description:

Enolates of carbonyl compounds will add to an α,β-unsaturated carbonyl compounds to give 1,5-dicarbonyl compounds. This is called the Michael reaction.

Notes: 

Enolates are excellent nucleophiles; although a second resonance form is present with the negative charge on oxygen, the resonance form with the negative charge on carbon tends to be more important for determining reactivity.

Examples:

Notes: Note that in each case a carbon-carbon bond is being formed

Mechanism:

Removal of a proton from the ketone with strong base (Step 1, arrows A and B) results in an enolate, which then performs a 1,4-addition on the α,β-unsaturated carbonyl compound (Step 2, arrows C and D), which is then protonated (Step 3, arrows E and F).

Notes:

Sodium here isn’t specifically important, it just balances out the negative charge.

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{ 5 comments… read them below or add one }

Daniel April 6, 2012 at 12:28 pm

Thanks for the numbering part James. It was driving me mad.
Plus, your tip of always making sure to count my Carbons really helps as well.

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james April 8, 2012 at 3:52 pm

It makes a big difference! Mistakes are really easy to make.

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Vicki April 10, 2014 at 2:01 pm

Thank you this is easy to follow. I actually understand what is going on.

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Smriti April 22, 2014 at 12:32 am

Thanks for numbering and this makes so much more sense!!!

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Fiona Liang April 23, 2014 at 11:25 pm

Hey James! Quick question:I read in Klein’s book that Michael donors have to be an enolate from a di-carbonyl compound (because it’s more stable and less reactive, etc) in order to be selective to strictly undergo 1,4-addition. Is steric hinderance the reason why 1,4-addition prefer to occur in this case?

Many thanks!

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