Regioselective C-2 or C-5 Direct Arylation of Pyrroles with Aryl Bromides using a Ligand-Free Palladium Catalyst

A simple and atom-economical procedure for the regioselective C-2 or C-5 arylation of pyrroles via a C-H bond activation is reported. Only 0.5-0.01 mol% of commercially available and air-stable ligand-free palladium(II) acetate [Pd(OAC)(2)] was employed as the catalyst. The presence of electron-withdrawing substituents such as formyl, acetyl or ester at the C-2 position of the pyrrole is tolerated. This environmentally attractive procedure has also been found to be tolerant to a very wide variety of functional groups on the aryl bromides such as formyl, acetyl, propionyl, ester, nitrile, nitro, fluoro, methoxy, amino or trifluoromethyl.