Palladium catalyzed C-H functionalization of O-arylcarbamates: Selective ortho -bromination using NBS

A series of cyclometalated palladium complexes derived from O-phenylcarbamates has been synthesized by the reaction of the respective carbamates with Pd(OAc) ₂ in the presence of acids, CF ₃CO ₂H, CF ₃SO ₃H, and p-TsOH. The palladacycles were observed to coordinate amines and electron rich anilines but not sulfonamides or carboxamides. Analysis of the ^tBu-NH ₂ adduct of the palladacycle 2b (2b• ^tBu-NH ₂) by NMR spectroscopy (NOE) revealed a cis-coordination of the amine. However, the amine adducts failed to undergo ortho-amination (C-N bond formation) under varied reaction conditions. Notably, the palladacycle 1d was found to react efficiently with N-iodosuccinimide (NIS) to yield the ortho-iodinated carbamate, 1e. More significantly, this reaction can be extended to a palladium-catalyzed ortho C-H bromination of aryl-O-carbamates even at 5 mol % loading of Pd(OAc) ₂ using N-bromosuccinimide (NBS).