Metal‐free para‐C−H Hydroxylation of Aryl‐urea Derivatives

The silica gel promoted straightforward remote para-C-H hydroxylation of aryl-urea derivatives under metal-free mild conditions by using diacetoxyiodobenzene as oxidant has been developed. Replacing the Lewis acids with silica gel effectively improved the tolerance of functional groups and resulted in a wide range of target compounds with various substituents in moderate to excellent yields. Moreover, this transformation has been demonstrated that could more effectively and conveniently synthesize pharmaceutical and biomedical compounds which contain 4-hydroxyarlyurea skeleton.