Michael Addition? It's Easy If You Do It Smart

Michael Addition? It's Easy If You Do It Smart

Michael Addition is a very well known reaction in organic chemistry and it involves a new carbon-carbon bond formation. What you should know that it incorporates active methylene group as a nucleophile and an alpha-beta unsaturated carbonyl compound. Voila !! yes, you are smart enough if you have identified how you can synthesize that alpha-beta unsaturated carbonyl compound; yes, you can cross check it right here if you are thinking about aldol condensation.

Michael Addition? It's Easy If You Do It Smart

As of now, you already know that usually in Michael Addition, an active methylene group is incorporated you need to choose the reagent carefully. Active methylene group is a -CH2- group which is connected to two strong electron withdrawing groups, for example, nitro (-NO2), ester (-COOR'), nitrile (-CN), carbonyl (-CO) etc. functional groups. This active methylene group containing molecule is considered as Michael donor. On the other hand, the alpha-beta unsaturated carbonyl compound acts as Michael acceptor.

Michael Addition? It's Easy If You Do It Smart

Let us choose diethyl malonate (DEM) as the Michael donor. Diethyl malonate on treatment with triethylamine (TEA) undergoes deprotonation. The hydrogens connected to the active methylene of diethyl malonate are much acidic in nature that it can be deprotonated with a base even if the base is weak enough. Thus, diethyl malonate generates its conjugate base which is a carbanion at the site of active methylene group on treatment with triethylamine. The conjugate base of DEM is stabilized owing to the electron withdrawing inductive (-I) effect of the two ester groups attached to it.

Michael Addition

Michael Adduct formation

The carbanion generated from the Michael donor on treatment of base, acts as a nucleophile. This nucleophile attacks to the alkylidene moiety of the alpha-beta unsaturated carbonyl compound (Michael acceptor) and forces the pi electron to move on to the next carbon, an intermediate is generated out of this nucleophilic attack, which is an enolate. As the negative charge on oxygen comes back to make pi bond between carbon and oxygen, the pi bond between C-C shifts to the other C, forms a carbanion, and another resonating structure is obtained. In the consecutive resonance structures generated out of the pi electron movement involves 4 atoms (starting arbitrarily from atom positioned at 1 and ending at position 4 atom which is oxygen), hence, Michael addition is also known as 1,4-addition. In the next step, the carbanion is protonated by the conjugate acid of TEA that has been produced during the generation of the first carbanion nucleophile from DEM. and gives the final product of the reaction, also known as the Michael adduct

Michael Addition? It's Easy If You Do It Smart

As a consequence, in a Michael addition reaction, a new carbon-carbon bond is formed at the beta position to the the carbonyl group of the alpha-beta unsaturated carbonyl moiety, and thus Michael addition is a well known reaction for beta functionalization of the carbonyl containing compond.

Find the solution of the reaction in the image here,