Active methylene and methyne compounds can be chemoselectively brominated in high yields using potassium bromide, hydrochloric acid, and hydrogen peroxide at room temperature.Halogenated active methylene and methyne compounds are very important synthetic intermediates for the nucleophilic substitutions in synthetic organic chemistry. The classical methods of halogenation of active methylene and methyne compounds 1 are the reaction with bromine 1 or sulfuryl chloride, 2 however, they suffer from drawbacks such as toxicity of the reagents, generation of acidic gasses after the reaction, or overhalogenation of the aromatic rings in 1. Although a number of new methods of this transformation have previously been developed, most of them have severe disadvantages such as the production of undesirable waste. [3][4][5] Khan and co-workers recently developed chemoselective bromination of active methylene compounds by employing the vanadium pentoxide catalyzed (V 2 O 5 ) oxidation of ammonium bromide (NH 4 Br) by hydrogen peroxide (H 2 O 2 ). 5 The reaction conditions of this method are very mild, and the reaction affords a product in high yield with high chemoselectivity. However, there are still some problems such as the use of a toxic vanadium compound as the catalyst and dichloromethane as the solvent.We now describe the chemoselective bromination of 1 by potassium bromide, hydrochloric acid and 30% hydrogen peroxide in toluene (Scheme 1). This method provides the desired monobromide 2 in high yields, while producing only nontoxic potassium chloride and water as waste.During the course of our study of the tantalum(V)-catalyzed oxidation of halogen anions to halogen cation equivalents, 6-8 we found that 1,3-diphenylpropane-1,3-dione could be quantitatively monobrominated by treatment with TaCl 5 (0.1 equiv), KBr (8.0 equiv), H 2 O 2 (8.0 equiv) and aqueous HCl (8.0 equiv) in chloroform. 6 We further examined the reaction, and found that the monobrominated compound could be obtained in the absence of the tantalum(V) catalyst. The most appropriate conditions are the treatment of 1 with KBr (5.0 equiv), HCl (5.0 equiv), and H 2 O 2 (20.0 equiv) in toluene at room temperature with stirring by a magnetic stirrer (Table 1).Several compounds with general structure 1 were examined under the reaction conditions, and the monobrominated compounds 2 quantitatively obtained in most cases. These results are summarized in Table 2. It is notable that the aromatic ring (entries 1 and 2), the ester group (entries 3-6), the amide group (entries 1 and 2) were inert under the given reaction conditions. Unfortunately, allyl acetoacetate (1k) did not provide the desired compound but complex mixture (entry 8). In this case, the alkene part of 1k also might react with the bromonium ion equivalent. Furthermore, we found that the use of a mechanical stirrer instead of a magnetic stirrer is effective in driving the reaction. In the case of using a mechanical stirrer, 1 quantitatively reacted with KBr (1.0 equiv), HCl (1.0 equiv), and H 2 O 2 (1.2 e...