a, b - Unsaturated Carbonyl Compounds

Carbon-carbon double bond is deactivated towards electrophilic addition by the electron withdrawing carbonyl group. However, the double bond is activated towards nucleophilic addition. In electrophilic addition the intermediate is a cation. In nucleophilic addition the intermediate is an anion. Addition to the carbon-carbon double bond takes place with orientation of the negative addition species adding to the b-carbon and the positive species adding to the a-carbon.

Electrophilic addition

Nucleophilic addition

The Michael Addition

The Michael addition involves the formation of a carbanion through the abstraction of the acidic hydrogen (by a base) from the following three compounds.

Ethyl malonate:

Ethyl acetoacetate

Ethyl cyanoacetate

The nucleophile thus formed can then combine with an a, b-unsaturated carbonyl compound. For example:

The Diels-Alder Reaction

A cycloaddition of a conjugated diene and an a, b-unsaturated carbonyl compound.

For example:

Quinones are an example of a highly conjugated a, b-unsaturated carbonyl compound: