Regioselective Bromination of Fused Heterocyclic <i>N</i>‑Oxides

A mild method for the regioselective C2-bromination of fused azine <i>N</i>-oxides is presented, employing tosic anhydride as the activator and tetra-<i>n</i>-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 Ts<sub>2</sub>O/TBACl is also presented. Finally, this method could be incorporated into a viable one-pot oxidation/bromination process, using methyltrioxorhenium/urea hydropgen peroxide as the oxidant.