Regioselective bromination of activated aromatic substrates with a ZrBr4/diazene mixture

A regioselective method for the bromination of phenols, ethers and anilines using a ZrBr₄/diazene mixture is described. The reaction takes place under mild reaction conditions and the bromine atom adds first at the para unsubstituted position with respect to the OH, OR or NR₂ group of the activated aromatic substrate. Less reactive compounds such as toluene, phenyl acetate, benzonitrile and trifluoromethylbenzene remain intact under the same conditions.