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.