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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{ 8 comments… read them below or add one }

Daniel

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

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

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Vicki

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

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Smriti

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

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Fiona Liang

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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Naga veera

Usually more substituted alpha C of michael donar is involved in the addition. Even bulky base using. Is it right?

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HagiAzo

thank you James, the mechanism makes sense now, and the numbering is creally helpful…

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Neha

If 1,4- addition and 1,2- addition pathways are both possible, how do we decide which one the reaction actually goes through?

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