Synthesis of 2-Methylindoles through Ruthenium(II)-Catalyzed Reaction of Aniline Derivatives with Allylamines

The ruthenium(II)-catalyzed reaction of aniline derivatives with allylamines was carried out, affording 2-methylindoles via C-H/C-N bond activation. 4,5-Dimethyl pyrimidin-2-yl group attached on the nitrogen atom of anilines is the most effective directing group and N-allyl-4-fluoro-N-methylaniline is the optimal allylamine. The cyclization products were obtained in 16% to 96% yields. The method does not require external oxidant. A possible mechanism is proposed.