Iridium Complex-Catalyzed Cross-Coupling Reaction of Terminal Alkynes with Internal Alkynesvia CH Activation of Terminal Alkynes

The cross-dimerization of an electron-rich terminal alkyne with an electron-deficient internal alkyne was promoted by an iridium complex to produce a 1 : 1 adduct in high regio- and stereoselectivities. This reaction was extended to various combinations of terminal alkynes with internal alkynes such as alkynyl esters and alkynyl aldehydes. The selectivity of the reaction was found to markedly depend on the ligands used. When dppe was used as a ligand, the 1 : 2 cross-cyclotrimerization reaction took place to form substituted benzene derivatives. A plausible reaction path was suggested based on a labeling experiment. This reaction provides a method for the production of complicated enynes which are difficult to be prepared by conventional methods.