The Michael addition is a nucleophilic addition reaction between an enolate ion (or another nucleophile, such as an enamine) and an α,β-unsaturated carbonyl compound. This reaction is significant in synthesis because it allows for the formation of carbon-carbon bonds, which is a key step in constructing complex organic molecules. Furthermore, it introduces a new functional group into the molecule, which can be further manipulated in subsequent reactions to achieve the desired target structure.