DOI: 10.1002/adsc.201500700 Palladium-Catalyzed Formation of N-Heteroarenes from Nitroarenes using Molybdenum Hexacarbonyl as the Source of Carbon Monoxide Fei Zhou, +a Duo-Sheng Wang, +a and Tom G. Driver a,b, * a Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, IL 60607-7061, USA Fax: (+ 1)-312-996-9672; e-mail: tgd@uic.edu b Institute of Next Generation Matter Transformation, College of Chemical Engineering, Huaqiao University, 668 Jimei Blvd. Xiamen, Fujian, 361021, People)s Republic of China + Contributed equally to this project. Received: July 23, 2015; Revised: August 14, 2015; Published online: November 6, 2015 Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201500700. Abstract: The development of a method that em- ploys a two-chamber reaction vessel and uses mo- lybdenum hexacarbonyl [Mo(CO) 6 ] as the carbon monoxide (CO) source for the palladium-catalyzed transformation of nitroarenes into indoles or imida- zoles is reported. The scope and limitations of our method are illustrated with 23 examples. Experi- ments that indicate the mechanism of the C À H bond amination reaction to be stepwise are also re- ported. Keywords: carbon monoxide equivalent; imida- zoles; indoles; molybdenum; palladium The prevalence of the indole scaffold in compounds that exhibit important biological activities continues to spur research into developing reactions for its as- sembly. [1,2] Our group has developed methods [3] which construct the C À N bond through sp 2 -C À H bond ami- nation using an aryl azide as the nitrogen-atom source. [4,5] Because of the challenges of substrate syn- thesis and safety concerns with introducing the azide functional group, [6] we turned our attention toward developing metal-catalyzed processes that employed an alternative electrophilic nitrogen-atom source. We discovered that the combination of [Mo(CO) 6 ], phe- nanthroline and [Pd(OAc) 2 ] could trigger similar reac- tivity from a,b,b-trisubstituted nitrostyrenes to enable access to 3H-indoles (Scheme 1). [7] At the conclusion of this study, we were interested in determining if [Mo(CO) 6 ] could function as the reductant for the synthesis of heteroarenes, such as indoles. While these heterocycles have been synthesized from nitroarenes or nitroalkenes using [Pd(OAc) 2 ] and CO, [8,9] we be- lieved that using [Mo(CO) 6 ] as the reductant would provide a useful alternative to these methods because it is an easily weighable solid, whose use would obvi- ate the need to manipulate a gas. [10] To our surprise, when we exposed a-phenylnitrostyrene to [Mo(CO) 6 ], Scheme 1. Use of Mo(CO) 6 as the reductant in Pd-catalyzed 3H-indole formation. Adv. Synth. Catal. 2015, 357, 3463 – 3468 # 2015 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim 3463 COMMUNICATIONS