Metal triflate-catalyzed regio- and stereoselective Friedel-Crafts alkenylation of arenes with alkynes in an ionic liquid: Scope and mechanism

In the metal triflate-catalyzed hydroarylation of alkynes, employing an ionic liquid dramatically enhanced the catalytic activities, resulting in broadening the scope of substrates (arenes and alkynes). In some cases, even reactions that were not possible in conventional organic solvents proceeded smoothly in ionic liquids. Moreover, the ionic liquid phase containing catalyst could be readily recovered by simple decantation of the organic layer after reaction and reused for the following runs without any significant loss of activity. Mechanistic studies including C-13 NMR analysis of reaction intermediates and isotope experiments confirmed for the first time that this type of reaction proceeds via vinyl cationic intermediates.