Diazoacetate and Related Metal-Stabilized Carbene Species in MCRs

Metal-stabilized carbenes derived from metal-catalyzed decomposition of diazo compounds are among the most important species in modern organic synthesis. In recent years, metal carbenes have been successfully applied to a series of multicomponent reactions (MCRs) for synthesizing more complicated molecules. Diazoacetates are the most preferred substrates for generating stable metal carbene species. This chapter provides an overview of MCRs involving metal carbenes derived from diazoacetates. There are mainly three types of MCRs involving metal carbenes: (1) metal carbenes react with carbonyl compounds or imines to form carbonyl or azomethine ylides that further undergo 1, 3-dipolar cycloadditions with different types of dipolarophiles to afford five-membered heterocycles; (2) metal carbenes undergo nucleophilic attack from alcohols, amines, or nitrogen-containing aromatic heterocycles to generate protic onium ylides or zwitterionic intermediates, which further undergo electrophilic interceptions with different electrophiles to establish MCRs; and (3) MCRs involving metal carbene migratory insertion processes.