Dual activation with Fe(NTf2)3 and I2: Regioselective halogenation of aromatic compounds using N-halosuccinimides (NXS)

Abstract

Halogenation of a wide range of aromatic compounds catalyzed by Fe(NTf₂)₃ in the presence of a catalytic amount of I₂ using N-bromosuccinimide (NBS) or N-chlorosuccinimide (NCS) in MeCN was reported. Dual activation with Fe(NTf₂)₃ and I₂ was quite useful to accelerate the reactions. High para selectivity was realized for the halogenation of aromatic compounds possessing electron-donating groups. Solvent-free reactions were effective for the halogenation of electron-deficient compounds. Furthermore, this method was suitable for the bromination of the compounds possessing acid-sensitive groups such as acetal, dihydrofuran, aldehyde, and epoxide. In the bromination of phenol and aniline derivatives, BiCl₃ was suitable to give the corresponding bromides in excellent yields. The procedure was successfully applied to the late-stage halogenation of drugs and natural products. One-pot bromination/Suzuki-Miyaura cross-coupling reactions afforded the corresponding biaryls in good yields without the removal of MeCN. When BiCl₃ was used as the catalyst, one-pot bromination/Sonogashira coupling reactions gave the corresponding alkynes without the removal of MeCN. This method is practical because the catalysts are cheap and the reactions can be performed under ambient air conditions.