In Situ Anodically Oxidized BMIm-BF(4): A Safe and Recyclable BF(3) Source.

The anodic oxidation of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIm-BF(4)) efficiently generates BF(3) from BF(4)(-). This Lewis acid, strongly bound to the ionic liquids, can be efficiently used in classical BF(3)-catalyzed reactions. We demonstrated the BF(3)/BMIm-BF(4) 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 BF(3)-Et(2)O 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 BF(3) (no storing necessity) in the required amount, using only the electron as redox reagent, and the recycling of BMIm-BF(4) for multiple subsequent runs.