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-1-catalyzed imidazole N-arylation, the first Ullmann-type synthesis of N-mesityhmidazole (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. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).