Synthetic Approaches to Sterically Hindered N‐Arylimidazoles through Copper‐Catalyzed Coupling Reactions

Optimization studies allowed the efficient synthesis of a simple structural motif based on meta ‐bis(1‐imidazolyl)benzenes 1 through copper‐catalyzed coupling of 1,3‐diiodobenzene and imidazole under mild reaction conditions. This protocol was then used to prepare a representative sterically hindered N ‐arylimidazole 2a , the most common structural motif among N ‐heterocyclic carbenes (NHC). Having optimized the main variables governing Cu I ‐catalyzed imidazole N ‐arylation, the first Ullmann‐type synthesis of N ‐mesitylimidazole ( 2a ) is reported. Moreover, the coupling between boronic acids as the aryl donor partners and either imidazole or benzimidazole was examined; in all cases the reactions proceeded in very low yield. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)