K2S2O8-Promoted Consecutive Tandem Cyclization/Oxidative Halogenation: Access to 3-Halo-Pyrazolo[1,5-a]pyrimidines

Abstract

A one-pot methodology has been developed to synthesize 3-halo-pyrazolo[1,5-a]pyrimidine derivatives through the three-component reaction of amino pyrazoles, enaminones (or chalcone), and sodium halides. The use of easily accessible 1,3-biselectrophilic reagents like enaminones and chalcone offers a straightforward approach for the synthesis of 3-halo-pyrazolo[1,5-a]pyrimidines. The reaction proceeded through a cyclocondensation reaction between amino pyrazoles with enaminones/chalcone in the presence of K2S2O8 followed by oxidative halogenations by NaX-K2S2O8. Mild and environmentally benign reaction conditions, wide functional group tolerance, and scalability of the reaction are the attractive facet of this protocol. The combination of NaX-K2S2O8 is also beneficial for the direct oxidative halogenations of pyrazolo[1,5-a]pyrimidines in water.