Studies Of Transition-Metal-Catalyzed C-H Bond Activation

The development of methods for forming C-C and C-X bonds plays a central role in organic chemistry. Transition metal-catalyzed cross-coupling reactions, including Kumada, Heck, Suzuki-Miyaura, Stille and Sonogashira reactions, have emerged as a powerful methodology for the formation of C-C bonds over the past decades. However, since the need of using prefunctionalized starting materials, the discovery of efficient and environmentally benign methodologies is highly desirable. Transition metal-catalyzed C-H activation is the most powerful and straightforward strategy in synthetic chemistry because it offers highly efficient and atom-economic organic transformations for the construction of complex molecules. During the past two decades, many reports have been focused on the sp2C-H activation. However, much less research has been focused on the activation of sp3C-H bonds. We mainly investigated transition-metal catalyzed functionalization of sp3and sp2C-H bonds in this dissertation. The contents are as follows:1. FeCh Catalyzed Alkylation of Propargyl EthersIron (II) chloride catalyzed direct alkylation of sp C-H bond adjacent to oxygen in propargyl ethers has been accomplished by the use of2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as oxidant under mild reaction conditions. The reaction proceeded smoothly with a variety of1,3-diketones leading to (3-dicarbonyl ether in moderate yields. In the absence of1,3-diketones, ynenones were produced under very mild reaction conditions by the use of iron (III) chloride and DDQ.1H NMR indicates the obtained ynenones are E/Z mixtures and the major isomer is the E-isomer (confirmed by nuclear Overhauser effect spectroscopy).2. Pd-Catalyzed Arylation/Oxidation of Benzylic C-H BondA palladium-catalyzed benzylic C-H arylation/oxidation reaction leading to diaryl ketones has been accomplished. The indispensable role of the bidentate system is disclosed for this sequential process. Aryliodides with both electron-withdrawing and electron-donating groups presented good compatibility with the reaction conditions. The arenes with both electron-withdrawing substituents and electron-donating substituents on the para-position of the phenyl ring underwent this novel transformation to form the corresponding products in moderate to good yields. Further experiments showed that the directing group can be removed by hydrolysis under basic conditions to afford2-aminobenzophenone derivatives. This chemistry offers a direct new access to a range of diarylketones.3. Palladium-Catalyzed Coupling Reaction of Indoles with Benzoic Acids: Synthesis of C3-Benzolylation Biindolyl via Dual C-H Bond ActivationA palladium-catalyzed dual C-H bond activation reaction of indoles with benzoic acids has been developed. In the presence of catalytic palladium and a stoichiometric silver carbonate, benzoic acids smoothly undergo the coupling reaction with indoles, providing the corresponding C3-benzolylation biindole scaffolds.