Nucleophilic Fluorination Reactions Starting from Aqueous Fluoride Ion Solutions

The sulfonium borane 2+ reacts with fluoride anions in MeOH/H2O mixtures to afford the zwitterionic fluoroborate 2-F as an easily isolable nonhygroscopic solid. In dry acetonitrile, 2-F reacts with PhS− to afford the anionic fluoroborate 1-F−. The latter is very labile and acts as a nucleophilic fluorination reagent toward a variety of substrates including alkylhalides and electron-deficient aromatic compounds. This approach may become broadly applicable to nucleophilic fluorination procedures that involve wet fluoride sources.