Studies Of Rh-Catalyzed Alkenylation Of Indoles Via C-H Bond Activation

Indole is one of the most important heterocycle that widely used in pharmaceuticals, agrochemicals, and functional materials. In recent years, the photophysical property of indoles aroused great interest. Many researches demonstrate that the photophysical property of indoles has certain relationship with their structures. Hence, it's important to develop the efficient methods for modifying indoles in the degree of conjugation and the substituents.Transition-metal-catalyzed C-H bond activation using directing group is the powerful and straightforward tool in synthetic chemistry, because it offers highly efficient and atom-economic transformations for the synthesis of valuable organic motifs. Recent advances in the metal-mediated direct C-H alkenylation reactions of heteroarenes provide an efficient access to monoalkenylated indoles. However, a survey of reports on alkenylation of indoles demonstrates that the dialkenylation of indoles by dual C-H bond activation is rarely exploited. Herein, we study a one-pot synthesis of 2,4-dialkenylindoles by rhodium-catalyzed dual C-H bond alkenylation of indoles with alkenes, and thus carboxylic acid directing group was removed during the reaction process. Both acrylates and styrenes were good alkene substrates to give the diverse dialkenylated indoles. The preliminary study reveals that the substituents on the dialkenylindoles significantly influence the photophysical property of the indoles, and the quantum yield of 0.57 was achieved when the para-substituent on styryl group was methoxycarbonyl (2.5af), implying the potential of this compound to be used as fluorescent probes and materials in optoelectronic devices.