Lithium Aryltrifluoroborate as a Catalyst for Halogen Transfer

The catalysis of two successive bromine–lithium exchange reactions, referred to as a "halogen dance", by lithium aryltrifluoroborate is reported. At a loading of 10 mol %, this catalyst exhibited efficient activity for bromo group transfer and was applicable to various brominated pyridines. Density functional theory calculations were consistent with the proposed mechanism, where the catalyst provided a bromine atom to the mono- or dibrominated substrate and the resulting debrominated catalyst then abstracted another bromine atom from the di- or tribrominated substrate, leading to the transposition of the bromo group on the substrate with catalyst regeneration.