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

The formation of carbon-carbon bonds is of great importance in organic chemistry, and transition metals play important roles in the formation of carbon-carbon bonds. For example, transition metals-catalyzed Heck reaction, Suzuki-Miyaura reaction, Stille reaction, and Sonogashira coupling reaction are versatile tools for formation of carbon-carbon bonds. However, one main drawback of those methods is the requirement of the prefunctionalization of the substrates. Consequently, the development of transition metals-catalyzed C-H activation transformations provides the more efficient ways for the C-C bond construction, and the related reseach has aroused great interest. The reactivity and selectivity are the great challenges in C-H activation.This dissertation mainly focused on the studies of transition metal catalyzed C-H bond activation, which include:1. RuCl3-catalyzed peroxide-promoted regioselective arylation of 2-arylpyridines with aryl iodidesNitrogen-coordinating functional groups are usually employed to direct the arylation involving C-H activation and control the regioselectivity. We describe our findings regarding the direct arylation of aryl iodides and 2-arylpyridine in the presence of simple transition-metal salts using benzoyl peroxide as crucial promoter to generate the biarylated products in high yields. A variety of aryl iodides and 2-arylpyridine that incorporate electron-donating and electron-withdrawing groups, including chloro and bromo,were well tolerated. The arylation proceeded in comparable yield and efficiency when diverse heterocycles, including pyrazole, pyrimidine, pyridazine, and quinoline, were used as the directing groups. Compared to the reported catalytic system, the reactions could be performed in the absence of expensive ligands and did not require any precautions with regard to the exclusion of air and moisture, and biarylated products were obtained in high yields.2. RuCl3-catalyzed alkenylation of aromatic C-H bonds with terminal alkynesAlkenylation of arenes is among the most important transformations in organic synthesis. However, terminal alkynes are rarely used as alkenylation substrates in chelation-assisted aromatic C-H bond reactions. We report our efforts to develop a new catalytic method for the alkenylation of arylpyridines at the ortho C-H bond in the aryl ring with terminal alkynes in the presence of RuCl3 and benzoyl peroxide or/and benzoic acid. Markedly high stereoselectivity was obtained in good to high yields employing aryl alkynes with (E)-stereoisomers as the predominant alkenylation products. The alkyl alkynes were also suitable for the alkenylation reaction generating the products in (E)- and (Z)-stereoisomers. The scope of the alkenylation and arylation is broad and tolerates a variety of functional groups. The catalytic system could also be extended to the alkenylation of arylpyridines with allylic compounds, which provide new protocols for the synthesis of arylalkenes. In addition, the reaction was highly regioselective to give the monoalkenylated product without the suffering of double alkenylation. The combination of RuCl3 catalyst and benzoic acid also allowed the arylation of arylpyridines under the reaction conditions. Although the replacement of benzyl peroxide with benzoic acid led to the lower yields, the results were still valuable considering the benzoyl peroxide was not easy to handle at high temperatures.3. CuBr-mediated oxyalkylation of vinylarenes via cleavage of sp3 C-H Bonds a to oxygenVinylarenes are common intermediates, and their difunctionalization is an important objective in organic synthesis. Manipulation of C-H bonds in the difunctionalization of vinylarenes to form CX-CC bonds should have great synthetic potential. Herein, we report a new type of difunctionalization reaction of vinylarenes where CuBr catalyzes the regioselective oxyalkylation of vinylarenes through the cleavage of an sp3 C-H bond adjacent to the oxygen atom to give the a-carbonyled-p-alkylated aryl products in the presence of TBHP under mild aerobic conditions. This is an unprecedented reactivity mode for vinylarenes, in which the alkylation is spontaneously processed with the Wacker oxidation. Excellent regioselectivities and high functional group tolerance were observed in this transformation. The addition of the a-C-H bond of oxygen to vinylarenes yielded anti-Markovnikov alkylated products, and the oxidative carbonylation occurred at the a-position of vinylarenes. The method can be broadly applied to the synthesis ofβ-alkylated ketone.4. Pd(OAc)2-catalyzed C-3 arylation of indolizine substrate using organoboron reagents as electrophilesIndolizines are important aromatic heterocycles that serve as key components of a variety of biologically active molecules and functional materials. The traditional arylation of them often involves indolizines'C-3 halogenation and subsequent Suzuki-Miyaura cross-coupling. We develop a direct, one-step laststage methods of arylation of the indolizine core with aryl boronic acids using Pd(OAc)2/Ag2CO3/DMA system.. Arylboronic acids with electron-withdrawing groups afforded better yields, and ortho-substitution decrease the yield of the product obviously. Other function groups like methylthio, trifluoromethoxy and formyl are bearing in this catalysis system.