Halide-free highly-pure imidazolium triflate ionic liquids:Preparation and use in palladium-catalysed allylic alkylation

摘要

The reaction of three oxygenated heterocycles(tetrahydrofuran,tetrahydropyran,1,4-dioxane)with trifluoromethane sulfonic anhydride in the presence of the non-nucleophilic base poly(4-vinylpyridine)affords alkylditriflates quantitatively via ring opening.The alkylditriflates react with N-alkylimidazoles providing the bis-imidazolium bis-triflate salts in high yields.Hydroxymethyl substituted oxygenated heterocycles are converted into imidazolium triflate salts without opening of the heterocycle.Two imidazolium salts were characterized by X-ray crystallographic structure determination.The halide free ionic liquids were applied successfully as solvents in the palladium catalysed allylic alkylation.A co-crystal of 15 and tetrabutylammonium triflate has also been characterized by X-ray crystallographic structure analysis.