Halogenation of Pyrazolo[1,5-a]Pyrimidines with NXS

A series of halogenated systems for pyrazolo[1,5-a]pyrimidines have been developed. Selective transformations of pyrazolo[1,5-a]pyrimidines by mono- and di-iodination were achieved by varying the ratio of pyrazolo[1,5-a]pyrimidines to NIS. In addition, the reaction of pyrazolo[1,5-a]pyrimidines with NBS or NCS uniquely gave dibrominated or dichlorinated products. The wide range of substrates, good functional group tolerance and gram-scale synthesis further demonstrate the application potential of this reaction. This work provides an efficient method for the construction of structurally diverse halogenated pyrazolo[1,5-a]pyrimidine derivatives.