Base promoted direct C4-arylation of 4-substituted-pyrazolin-5-ones with diaryliodonium salts

A metal-free approach for the C4-arylation of 4-substituted-pyrazolin-5-ones with diaryliodonium salts was developed. The reaction proceeded smoothly at room temperature in the presence of DMAP (4-dimethylaminopyridine). As a result, a wide range of desired multi-substituted pyrazolin-5-one derivatives were obtained in good to excellent yields (20–98%).