Michael Addition
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Michael Addition
Conjugated carbonyl compounds are electrophilic. They can be attacked by nucleophiles in two ways. The carbonyl carbon can be attacked by a nucleophile in what is called 1,2-addition or the alkene can be attacked in what is called conjugate addition or 1,4-addition.
If an enolate is a nucleophile, 1,4-addition occurs. This is called a Michael Addition. Here is one example:
The enolates in a Michael Addition are called Michael donors and the conjugated carbonyl compounds are called Michael acceptors.
Michael donors and acceptors
Another example:
For the mechanism of the Michael Addition, an enolate attacks a conjugated carbonyl in a 1,4-addition. The electrons move all the way up to the oxygen atom making a negatively charged oxygen atom. The electrons come back down, and the pi bond grabs a proton from the solvent making a single bond.
Often, the Michael Addition stops at this point. But, if an ester is used as the enolate, it can be hydrolyzed with acid and heat to make carboxylic acids. Since we now have a carboxylic acid beta to a carbonyl, this particular molecule can decarboxylate giving the final product.
Overall:
11. When cyclohexenone reacts with hydroxide base, it undergoes a Michael addition. The cylohexenone acts as both the Michael donor and Michael acceptor. Draw the product of this Michael addition.
12. Draw the product of the following Michael addition reaction.
Answers
11.
12.
