The
1,4-conjugate addition reaction between activated alkynes or
acetylenic Michael acceptors and nucleophiles (i.e., the nucleophilic Michael reaction) is a historically useful organic
transformation. Despite its general utility, the efficiency and outcomes
can vary widely and are often closely dependent upon specific reaction
conditions. Nevertheless, with improvements in reaction design, including
catalyst development and an expansion of the substrate scope to feature
more electrophilic alkynes, many examples now present with features
that are congruent with Click chemistry. Although several nucleophilic
species can participate in these conjugate additions, ubiquitous nucleophiles
such as thiols, amines, and alcohols are commonly employed and, consequently,
among the most well developed. For many years, these conjugate additions
were largely relegated to organic chemistry, but in the last few decades
their use has expanded into other spheres such as bioorganic chemistry
and polymer chemistry. Within these fields, they have been particularly
useful for bioconjugation reactions and step-growth polymerizations,
respectively, due to their excellent efficiency, orthogonality, and
ambient reactivity. The reaction is expected to feature in increasingly
divergent application settings as it continues to emerge as a Click
reaction.