In SituAnodically Oxidized BMIm-BF4: A Safe and Recyclable BF3Source

Abstract

The anodic oxidation of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIm-BF4) efficiently generates BF3from BF4-. This Lewis acid, strongly bound to the ionic liquids, can be efficiently used in classical BF3-catalyzed reactions. We demonstrated the BF3/BMIm-BF4reactivity 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 thein situgeneration of BF3(no storing necessity) in the required amount, using only the electron as redox reagent, and the recycling of BMIm-BF4for multiple subsequent runs.