Michael Addition

Michael addition is a well known name reaction which involves a michael donor – generally an enolate (a nucleophile), and a michael acceptor – generally a conjugated system with an electron withdrawing group such as cyano, keto or ester (an electrophile).

Michal Addition with a michael acceptor and a michael donor - examples of reactants

Michal Addition with a michael acceptor and a michael donor - examples of reactants

The reaction generally proceeds under base catalysis as will be shown in the following mechanism. Michael addition is a great tool which can be used by organic chemists to increase the number of carbons of a molecule and make larger molecules by formation of new carbon-carbon bonds.

Mechanism

Step 1

In the first step, an enolate (or michael donor) is produced in the precence of a base by the abstraction of the alpha hydrogen of the carbonyl containing compound.

Step 1 - Formation of enolate (michael donor) in presence of base

Step 1 - Formation of enolate (michael donor) in presence of base

Step 2

In step 2, the michael donor (enolate) reacts with the michael acceptor to produce the molecule as shown. This leads to formation of a new carbon-carbon bond.

Step 2 - Reaction of the michael acceptor and michael donor

Step 2 - Reaction of the michael acceptor and michael donor

Step 3

In the final step, there is regeneration of the base catalyst by the carbanion formed in step 2 to form the final product.

Step 3 - Recovery of base by releasing the proton to the carbanion

Step 3 - Recovery of base by releasing the proton to the carbanion

Example of Michael Addition

A very good example of Michael Addition is the reaction of diethyl malonate (Michael Donor) with cyclohexenone (Michael Acceptor) in the presence of base sodium ethoxide. The reaction proceeds as shown and joins the two molecules by formation of a carbon-carbon bond.

Reaction of diethyl malonate (michael donor) with cyclohexenone (michael acceptor) to produce a new carbon-carbon bond and larger molecule.

Reaction of diethyl malonate (michael donor) with cyclohexenone (michael acceptor) to produce a new carbon-carbon bond and larger molecule.

Books on Organic Chemistry

Check out some of the best textbooks for Organic Chemistry

References

  1. Advanced Organic Chemistry: Reactions and synthesis. By Francis A. Carey, Richard J. Sundberg
  2. Organic Chemistry, 6th Edition. By Robert T. Morrison and Robert N. Boyd
  3. Organic-Chemistry.org – http://www.organic-chemistry.org/namedreactions/michael-addition.shtm (accessed on April 24, 2011)

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