Iron-catalyzed Functionalization Of Indoles At The C3-position

In this paper, reviews about the functionalization of indoles at C3(sp2)-H p osition in which no activating group was attached, iron-catalyzed cross-dehydrog enative coupling (CDC) reaction and free radical reactions were introduced. Be sides, we demonstrated the strategy about synthesis of C3-alkylatedindole in the presence of FeCl2 as catalyst. The article was expounded via three sections:Indole and derivatives are versatile precursors or intermediates in so many natural products and biologically active compounds. Moreover, they play an important role in medicine, agriculture, dyes, perfumes and other fields. Significantly, indole skeleton has become the most representative structure and drug groups in medicine, and more than 40 drugs have applied in different fields successfully. Traditionally, the synthesis of functionalization of indoles at the C3(sp2)-H position depended on the reaction between substrate and activating group (such as halogen, OTf, etc.) at the C3 position. With the development of catalysts about metal and small molecule in organic chemistry, some direct functionalization of indole C3(sp2)-H could be completed through metal or small molecule-catalyzed systems.Iron is not only the most abundant transition metal in the earth’s crust but also one of the earliest metal catalysts in organic chemistry. In addition, iron compounds are widely distributed in different biological systems. As one of green and efficient catalysts in organic chemistry, iron catalysts have been applied in various organic transformations nucleophilic additions, substitutions and oxidations. In particular, iron draws so much attention in the scope to construct C-C and C-heteroatoms in CDC reaction. The direct method to achieve functional substrates not only develops the overall efficiency and atom economy, but also provides a possibility to cheap, green, efficient strategy for industrial production.Based on those excellent research, an efficient method for synthesis of 3-alkylated indoles via the oxidative cross-coupling reaction of diphenylmethanederivatives C(sp3)-H with indoles C(sp2)-H at the C3-position was achieved employing the N,N-dimethylcarbamoyl moiety as auxiliary group in the presence of FeCl2 and 2,3-dichloro-5,6-dicyanoquinone (DDQ).In this thesis, the concept of strategy and experiment including optimization and characterization were summarized and presented. The cheap, green method could provide efficiency with good applicability and high selectivity.