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Palladium‐Catalysed Direct Polyarylation of Pyrrole Derivatives

The palladium‐catalysed direct polyarylation of 1‐methylpyrrole and 1‐phenylpyrrole was studied. As the C2 and C5 positions of pyrroles are more reactive for CH bond functionalisation than the C3 and C4 positions, the formation of 2,5‐diarylpyrroles was found to proceed selectively in the presence of 3 equiv. of a variety of aryl bromides. The sequential C2 arylation followed by C5 arylation to prepare non‐symmetrically substituted 2,5‐diarylpyrroles was also studied. For the synthesis of such pyrroles, higher yields were obtained for the couplings with electron‐deficient aryl bromides. The tetraarylation of 1‐methylpyrrole was also achieved. From 4 equiv. of 3,5‐bis(trifluoromethyl)bromobenzene, the 2,3,4,5‐tetraarylated pyrrole was obtained in good yield.