Peripheral cross-coupling of the enol form of the 5-pyrazolone
scaffold with arylboronic acids promoted by [PdCl2(dppf)] 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.
Suzuki-Miyaura - tautomers - pyrazolone - peripheral arylation - arylpyrazole