Palladium-catalyzed peripheral arylation of 5-pyrazolones via enolizable bond protection

Peripheral cross-coupling of the enol form of the 5-pyrazolone scaffold with arylboronic acids promoted by [PdCldppf)] afforded the arylated products in good yields. In this coupling, the protection of the enolizable hydroxyl group of pyrazolone is a prerequisite for ensuring the Suzuki-Miyaura cross-coupling. A particular feature of this process is that it enables the synthesis of 5-hydroxy-3-biphenyl and -terphenylpyrazole derivatives with structural diversity.