Research On Radical-based C-H Bond Activation Cross-coupling Reactions

C-H bond is one of the most basic chemical bonds of organic compounds. Cross-coupling reaction through C-H bond activation is challenging topic in modem synthetic chemistry. Compared with the commonly metal-catalyzed C-H bond activation, metal-free C-H bond activation has the advantages of high utilization rate of atoms, avoiding the pre-functionalization of substrates, which are according with the requirement of green chemistry. It is also more challenging and significant, and gradually attracts more attention from chemists.In this paper, di-tert-butyl peroxide promoted C-H bond oxidative functionalization under metal-free conditions was conducted. In detail, the following two kinds of reactions were investigated:C (sp3)-H oxidative functionalization for the reaction of indole or its derivatives with cycloalkane and C (sp2)-H oxidative functionalization for the reaction of Bunte salt (organic thiosulfate) with benzaldehyde or its derivatives. The mixture of indole or its derivatives and DTBP (mole ratio of 1:1.5), using cyclohexane as the solvent, was heated to 140℃ for 12 hours under the protection of nitrogen, affording the cyclohexyl substituted indole derivatives with the yield of 54% to 87%. The electrical properties of substituents could hardly give any influence on the regioselectivity, but the yields of products by using electron-rich substrates were lower than that using electron-deficient indoles. Affected by orientation effect of substituents,2,4 and 7-position were mainly functionalized. This method also applied to other cycloalkanes, such as cyclopentane, cycloheptane, cyclooctane and cyclododecane.Six kinds of Bunte salt were synthesized by the reaction of halogenated hydrocarbon and sodium thiosulfate. Then reacted with benzaldehyde or its derivatives under the optimal reaction condition, affording a series derivatives of S-substituted thiobenzoates, the yield was 69% to 77%. With the help of DTBP, aldehyde radicals could react with Bunte salt smoothly. Using Bunte salt as a source of sulfur to replace some odorous substance such as thiol, is a new method for the synthesis of derivatives of S-substituted thiobenzoates.