NBS/Carboxylic Acid Combination: Efficient Access To α,β-dibromination Of Carbonyl Compounds

Dihalogenated organic compounds are important synthetic intermediates in the manufactur e of Pharmaceuticals, agrochem-icals and other speciality chemicals. The reactions of unsaturated carbon-carbon bonds with halogens are widely used for the preparation of dihalogenated products. However, due to its toxic, corrosive and volatile nature, the use of elemental bromine is troublesome and environmentally hazardous, which heavily limits its applications. Therefore, it is necessary to develop new (di)bromination protocols.N-halosuccinimide (NXS), as a versatile reagent, can be used as a mild source of dihalogenation, in addition to monohalogenationas a common bromogenated reagent is a handleable and safe reagent in the bromogenated reaction. In this thesis, a mild, efficient and practical method for the preparation of dihalogenated products has been developed. Benzoic acid (0.2equiv.) is capable of catalyzing the reactions of unsaturated carbonyl compounds with N-halosuccinimides (NXS, X=Br and Cl) to afford a series of dihalogenated products at room temperature. The halogen bond interaction between NBS and benzoic acid leads to the formation of HBr, and thus, elemental bromide was generated in situ by further reaction with NBS.In conclusion, the combination of NBS and carboxylic acid has been, for the first time, used as a dibromination agent in the reaction with unsaturated compou nds. The reaction features mild conditions and is readily scalable and environmentally benign.