Abstract
The anodic oxidation of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIm-BF4) efficiently generates BF3 from BF4–. This Lewis acid, strongly bound to the ionic liquids, can be efficiently used in classical BF3-catalyzed reactions. We demonstrated the BF3/BMIm-BF4 reactivity in four reactions, namely, a domino Friedel–Crafts/lactonization of phenols, the Povarov reaction, the Friedel–Crafts benzylation of anisole, and the multicomponent synthesis of tetrahydro-11H-benzo[a]xanthen-11-ones. In comparison with literature data using BF3-Et2O in organic solvents, in all the presented cases, analogous or improved results were obtained. Moreover, the noteworthy advantages of the developed method are the in situ generation of BF3 (no storing necessity) in the required amount, using only the electron as redox reagent, and the recycling of BMIm-BF4 for multiple subsequent runs.
Highlights
The anodic oxidation of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIm-BF4) efficiently generates BF3 from BF4−
Boron trifluoride is a well-known Lewis acid, often used in organic synthesis to carry out many acid-catalyzed transformations.[1]
Catalyzed reactions in anodically oxidized BMIm-BF4, being this ionic liquid (IL) really easy to recycle after ethereal extraction
Summary
The anodic oxidation of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIm-BF4) efficiently generates BF3 from BF4−. Catalyzed reactions in anodically oxidized BMIm-BF4, being this IL really easy to recycle after ethereal extraction. We tested the anodically generated BF3 in BMIm-BF4 in this reaction, and the results are reported, along with the corresponding literature data, for a useful comparison.
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