Regioselective Bromination of Fused Heterocyclic N-Oxides

A mild method for the regioselective C2-bromination of fused azine N-oxides is presented, employing tosic anhydride as the activator and tetra-n-butylammonium bromide as the nucleophilic bromide source. The C2-brominated compounds are produced In moderate to excellent yields and with excellent regioselectivity in most cases. The potential extension of this method to other halogens, effecting C2-chlorination with Ts2O/TBACI Is also presented. Finally, this method could be incorporated Into a viable one-pot oxidation/bromination process, using methyitrioxorhenium/urea hydropgen peroxide as the oxidant.