Selective Monobromination of 1,3-Diones with N-Bromosaccharin/Mg(ClO4)2 System in Solution and under Solvent-Free Conditions

N-Bromosaccharin/Mg(ClO4)(2) is an effective and regioselective system for alpha-monobromination of 1,3-dicarbonyl compounds. A wide variety of beta-keto esters and 1,3-diketones in reaction with this system afforded a regioselectively alpha-monobrominated products. The bromination reaction can be conducted at 0-5 degrees C either in solution or under solvent-free conditions.