Palladium (II) - Catalyzed C3-Selective Friedel-Crafts Reaction of Indoles with Aziridines

The [PdCl2(MeCN)2]-catalyzed C3-selective Friedel-Crafts reaction of 2,2-disubstituted and 2-aryl-N-tosylaziridines with indoles is reported. For the 2,2-disubstituted substrates, [PdCl2(MeCN)2] alone, without any ancillary ligands, is an efficient catalyst for the ring-opening reaction. The presence of 1,4-benzoquinone as an additive was found to enhance the ring-opening reaction of the less-reactive 2-arylaziridines. This reaction displayed a broad substrate scope with respect to the indole substrate and is operationally simple. Finally, when 1,3-dimethylindole was employed as a substrate, the de-aromatized pyrroloindoline product was obtained in high yield and good diastereoselectivity.