| The compounds containing indole skeleton are ubiquitous in nature, many of its derivatives exhibit a well-defined pharmacological activity, and several of them have been used in clinic. Furthermore, analogs based on indole are significant players in a diverse array of markets such as dyes, plastics, agriculture, vitamin supplements, over-the-counter drugs, flavor enhancers, and perfumery. Among these compounds,2-vinylindoles, as an important branch of indole compounds, have shown great bioactivities, such as, antibiotics, anticancer activity; moreover, they are important building blocks for various medical intermediates and functional materials, and can be used for synthesis indole alkaloids and indolocarbazoles through [4+2] reactions; also they can be used for optical material by intermolecular metal-catalyzed C-H bond activation reaction.Indole regioselective C-H functionalization represents an important challenge in this area. In contrast to the much more developed C-H arylation reactions, direct alkenylations have received much less attention. A particularly challenge is the intermolecular direct alkenylation at the C2-position, for which only eight protocols have been reported. In spite of these important advances, some challenging issues still remain:for example,(i) a large excess of oxidants was used;(ii) stoichiometric amounts of the reduced external oxidant were produced as waste; and (iii) substrate scope was limited and some cases poor yields were obtained.In this chapter, we have developed a general, simple and efficient method for the intermolecular direct C-2alkenylation of indoles using palladium (Ⅱ) as catalyst and oxygen as the oxidant. The reaction not only can proceed well without Cu (Ⅱ), but shows complete regio-and stereoselectivity. All products are E-isomers at the C-2position, and no Z-isomers and3-substituted products can be detected on analyzing the reaction mixtures. The method should have many applications in organic and medical chemistry. |
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