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

Abstract

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.