N-Halosuccinimide/BF3−H2O, Efficient Electrophilic Halogenating Systems for Aromatics

Abstract
N-Halosuccinimides (NXS, 1) are efficiently activated in trifluoromethanesulfonic acid and BF3−H2O, allowing the halogenations of deactivated aromatics. Because BF3−H2O is more economic, easy to prepare, nonoxidizing, and offers sufficiently high acidity (−H0 ≈ 12, only slightly lower than that of trifluoromethanesulfonic acid), an efficient new electrophilic reagent combination of NXS/BF3−H2O has been developed. DFT calculations at the B3LYP/6-311++G**//B3LYP/6-31G* level suggest that protonated N-halosuccinimides undergo further protosolvation at higher acidities to reactive superelectrophilic species capable either in the transfer of X+ from the protonated forms of NXS to the aromatic substrate or in forming a highly reactive and solvated X+ which would readily react with the aromatic substrates. Structural aspects of the BF3−H2O complex have also been investigated.