Bromination of Ketones with H2O2—HBr “On Water”.

Various 1,3-diketones, β-ketoesters, cyclic ketones, aryl alkyl and dialkyl ketones were effectively brominated with an aqueous H2O2–HBr system “on water” at room temperature without the need for a catalyst or organic solvent. The resultant brominated ketones were isolated in yields of 69–97% with high selectivity for monobromination vs. dibromination. Reactivity was manipulated by using more diluted aqueous solutions of H2O2 and HBr and the use of an excess of HBr where necessary. Dilution also increases selectivity of ring bromination vs. α-bromination of aryl ketones with an activated phenyl ring. Finally, an aqueous H2O2–HBr system was used for a tandem oxidation–bromination process and alcohols were transformed into α-bromoketones. This simple but effective “on water” bromination of ketones with an aqueous H2O2–HBr system is characterised by the use of inexpensive reagents, a lower impact on the environment and the absence of organic waste that make it a good alternative to existing bromination methods.