Regiocontrolled Synthesis of 1,2‐Diaryl‐1H‐imidazoles by Palladium‐ and Copper‐Mediated Direct Coupling of 1‐Aryl‐1H‐imidazoles with Aryl Halides under Ligandless Conditions

Abstract

AbstractA large variety of 1,2‐diaryl‐1H‐imidazoles, including a selective COX‐2 inhibitor, have been regioselectively synthesised in moderate to high yields by direct coupling of 1‐aryl‐1H‐imidazoles with aryl iodides or bromides in DMF in the presence of CsF and catalytic amounts of Pd(OAc)2 under ligandless conditions. A possible mechanism for this new highly regioselective C‐2 arylation reaction, involving the formation of an organocopper(I) derivatives followed by a transmetallation reaction with an arylpalladium(II) halide species and a reductive elimination, is proposed. New one‐step procedures for the synthesis of 1,2,5‐triaryl‐1H‐imidazoles, based on palladium‐ and copper‐mediated arylation of 1‐aryl‐1H‐imidazoles, have also been developed. Interestingly, some imidazole derivatives prepared in this study have been found to exhibit significant cytotoxic activity against some human tumour cell lines. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)