K 2 S 2 O 8 -Promoted Consecutive Tandem Cyclization/Oxidative Halogenation: Access to 3-Halo-Pyrazolo[1,5- a ]pyrimidines.

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 K 2 S 2 O 8 followed by oxidative halogenations by NaX-K 2 S 2 O 8 . 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-K 2 S 2 O 8 is also beneficial for the direct oxidative halogenations of pyrazolo[1,5- a ]pyrimidines in water.