Regioselective Bromination of Fused Pyridine N-Oxides

Baran et al. have reported the regioselective bromination of fused pyridine N-oxides. According to their results, various C2-brominated fused pyridines are produced in high yields with high regioselectivity by using p-toluenesulfonic anhydride as the activator and tetrabutylammonium bromide as the nucleophilic bromide source. This reaction proceeds under mild conditions without commonly-used highly reactive brominating reagents such as Br₂ or POBr₃. This synthetic method can be incorporated into a viable one-pot oxidation/bromination process, using methyltrioxorhenium/urea hydrogen peroxide as the oxidant. Furthermore, high C2-selective chlorination can be also accomplished by using tetrabutylammonium chloride.