Ruthenium/Halide Catalytic System for CC Bond Forming Reaction between Alkynes and Unsaturated Carbonyl Compounds

A ruthenium complex [triruthenium dodecacarbonyl, Ru3(CO)12] in the presence of bis(triphenylphosphine)iminium chloride ([PPN]Cl) catalyzes the conjugate addition of terminal alkynes to alkyl acrylates to give high yields of γ,δ‐alkynyl esters. On the other hand, the linear codimerization reaction of terminal alkynes with alkyl acrylates proceeds in the presence of a catalytic amount of Ru3(CO)12 and lithium iodide to give the corresponding conjugate dienes. These two different types of catalytic carbon‐carbon bond forming reactions are controlled only by the nature of halide ions, either a chloride or an iodide, with other conditions being kept almost the same.