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Regioselective Bromination of Fused Heterocyclic N‑Oxides

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journal contribution
posted on 15.02.2013 by Sarah E. Wengryniuk, Andreas Weickgenannt, Christopher Reiher, Neil A. Strotman, Ke Chen, Martin D. Eastgate, Phil S. Baran
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/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.