Development of Catalytic Carbene Transfer Reactions Using Alkynes as a Source of Carbenes

The in situ generation of vinylidene and alkylidene complexes based on the activation of alkynes with transition metal compounds was investigated. The cyclic oxacarbene complexes are produced through the formation of vinylidene complexes followed by the electrocyclization with the neighboring subunit of ail alkyne. During the course of the study, it was found that a transition metal-induced 5-exo-dig cyclization of alkynes having nucleophilic conjugate subunits affords new types of hetero arene-substituted carbene complexes, such as (2-furyl)-, (2-pyrroryl), and (2-thienyl)carbene complexes. The 5-exo-dig cyclization of propargyl esters followed by 1,2-migration of carboxylates leads to the formation of vinylcarbene complexes. The in situ generation of metal-carbenoid species is highly atom-efficient and widely applicable to organic syntheses. In this account, the in situ generation of carbenoid species from a range of alkynes and synthetic applications to catalytic carbene transfer reactions, such as cycloaddition, annulation, ylide-associated reactions, insertion reactions, cycloisomerization, and isomerization reactions are highlighted and reviewed.