Indole synthesis: palladium-catalyzed C-H bond amination via reduction of nitroalkenes with carbon monoxide

Nitroalkenes have been called 'chemical chameleons' due to their versatility in numerous Synthetic transformations. Herein, we describe the first transition metal-catalyzed transformation Of conjugated nitroalkenes into indoles. Under mild reaction conditions (1 atm carbon trionoxide, 110 degrees C), palladium catalyzes the reductive cyclization of nitroalkenes to form a Putative nitrosoalkene intermediate, which then rearranges to provide 3-arylindoles in high yields, Notably, this novel C-H bond amination takes advantage of carbon monoxide as an inexpensive stoichiometric reductant and produces carbon dioxide as the major byplocluct. (C) 2008 Elsevier Ltd. All rights reserved.