Efficient and highly regioselective direct C-2 arylation of azoles, including free (NH)-imidazole, -benzimidazole and -indole, with aryl halides

The Pd- and Cu-mediated reaction of a large variety of pi-electron sufficient heteroarenes, which include free (NH)-imidazoles, -benzimidazole and -indole, with aryl iodides under ligandless and base-free conditions provides regioselectively the required 2-arylhetero-cycle derivatives in high yields. 2-Aryl-1-phenyl-1H-imidazoles can also be prepared by a one-pot domino HALEX and Pd- and Cu-mediated arylation reactions of 1-phenyl-1H-imidazole with activated and unactivated aryl bromides under base-free and ligandless conditions. The protocol for the synthesis of 2-arylazoles involving the use of aryl iodides has been found to be suitable for the efficient preparation of three bioactive compounds and a key intermediate in the synthesis of a heparanase inhibitor. (c) 2007 Elsevier Ltd. All rights reserved.