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

A one-pot methodology has been developed to synthesize3-halo-pyrazolo[1,5-a]pyrimidine derivatives throughthe three-component reactionof amino pyrazoles, enaminones (or chalcone), and sodium halides.The use of easily accessible 1,3-biselectrophilic reagents like enaminonesand chalcone offers a straightforward approach for the synthesis of3-halo-pyrazolo[1,5-a]pyrimidines. The reaction proceededthrough a cyclocondensation reaction between amino pyrazoles withenaminones/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 arethe attractive facet of this protocol. The combination of NaX-K2S2O8 is also beneficial for the directoxidative halogenations of pyrazolo[1,5-a]pyrimidinesin water.