Palladium-catalysed direct diarylations of pyrazoles with aryl bromides: a one step access to 4,5-diarylpyrazoles

The palladium-catalysed direct arylation of pyrazoles with aryl halides, using PdCl(C3H5)(dppb)/KOAc catalyst, reveals a similar reactivity of C4 and C5 CH bonds of pyrazoles, whereas the C3 CH bond is almost unreactive, and gives access in one step to a variety of 4,5-diarylpyrazoles. This CH bond functionalisation reaction tolerates a variety of substituents on the aryl bromide such as nitro, cyano, formyl, propionyl, ester, chloro, fluoro or trifluoromethyl groups.