Cross-coupling of 1-aryl-5-bromopyrazoles: regioselective synthesis of 3,5-disubstituted 1-arylpyrazoles

The cross-coupling of 1-aryl-5-bromopyrazoles 4 with alkynes, vinyltins and arylboronic acids promoted by Pd(PPh3)4 afforded unsymmetrical 3,5-disubstituted 1-arylpyrazoles 5-8 in excellent yields. 1-Aryl-5-bromopyrazoles 4 were prepared from their corresponding 1-arylpyrazolones 3 with PBr3 in refluxing acetonitrile.