Three-Coordinate Iron(0) Complex-Catalyzed Regioselective C-H Alkylation of Indole Derivatives.

The synthesis of alkylated indoles, which are key intermediates for various drugs and bioactive molecules, is of great importance. However, most reports on the synthesis of functionalized indoles use toxic and expensive 4d or 5d metal catalysts, limiting the further application of these methods. Herein, we disclose a versatile regioselective C-H alkylation of indole derivatives using a well-defined three-coordinate iron(0) complex. Neither Grignard reagents nor additional additives are required, making the reaction sustainable, environmentally friendly, and compatible with a broad variety of functional groups to afford C2-alkylated indoles in high yields. In addition, by variation of the aryl substituent on the alkene substrate to the trisubstituted silyl group, the regioselectivity of the C-H alkylation can be altered from Markovnikov to -Markovnikov. Detailed mechanistic studies further revealed the catalytic mode of reaction.