Mg(BF4)2 doped in [BMIm][BF4]: A homogeneous ionic liquid-catalyst for efficient synthesis of 1,8-dioxo-octahydroxanthenes, decahydroacridines and 14-aryl-14H-dibenzo[a,j]xanthenes

A homogeneous ionic liquid made up of 0.5 mol% Mg(BF4)2 doped in [BMIm]BF4 was obtained from a mixture of MgCl2 and [BMIm]Cl subjected to anion exchange with NaBF4. The ionic liquid efficiently catalyzes the synthesis of 1,8-dioxo-octahydroxanthenes, 14-aryl-14H-dibenzo[a,j]xanthenes, and 1,8-dioxo-decahydroacridines, giving excellent yields in short periods of time at 80 °C. The integrity of the ionic liquid remains reasonably unchanged when it is separated from the reaction mixture by water extraction, as it can be recycled several times without any loss of activity in each of the title syntheses. Magnesium cation, though in low concentration, appeared as an essential element of this ionic liquid catalysis, perhaps due to its non-coordinated existence giving rise to a promoted Lewis acidic characteristic. Application of this new homogeneous catalyst system offered the advantages of high yields, short reaction times, and easy workup procedure compared to the conventional methods of the syntheses.

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► A novel room-temperature imidazolium ionic liquid doped with Mg2+ cation was prepared.
► Exchanging Cl− of the IL with BF4− enhanced the catalytic activity of the dopant Mg2+.
► It offered the dual benefits of catalyst and solvent in the trial organic syntheses.
► The integrity of the ionic liquid virtually remains unchanged after recycling.