Palladium-catalyzed regioselective halogenation of aromatic azo compounds

Article abstract of DOI:10.1002/adsc.201200902

A highly regioselective halogenation reaction of symmetrical and unsymmetrical aromatic azo compounds has been developed at room temperature or at 50 °C. In the presence of 5 mol% palladium diacetate and 0.5 equiv. of p-toluenesulfonic acid, a range of symmetrical aromatic azo compounds smoothly undergo monobromination with N-bromosuccinimide to give the corresponding unsymmetrical aromatic azo compounds in good to excellent yields with >99:1 ortho-selectivity. This chemistry has been successfully extended to unsymmetrical aromatic azo compounds, whose electronricher aryl groups prefer to be monobrominated. Moreover, replacing N-bromosuccinimide with Niodosuccinimide in the reaction allows the synthesis of monoiodinated aromatic azo compounds with >99:1 regioselectivity.