Treatment of Olefinic Amides with NBS in Water: Synthesis of Monobromo- and Multibromobenzoxazines

Treatment of olefinic amides with N-bromosuccinimide (NBS) in water is reported. Monobromobenzoxazines were mainly formed at room temperature, while at 80 °C multibromobenzoxazines were preferentially generated. Mechanism studies showed that the reaction might proceed via a cascade of electrophilic addition at the C=C bond followed by electrophilic substitution at the aromatic ring. No additives are required in this protocol.