Studies Of Palladium-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 drawbacks of those methods are 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 palladium catalyzed C-H bond activation, which include:1. Pd(OAc)2-Cu(OAc)2 cocatalyzed direct C-2 arylation of indoles with potassium aryltrifluoroborate saltsThe C-arylated indoles are important building blocks of bioactive molecules, natural products, and pharmaceuticals. We studied the direct arylation of indoles with potassium aryltrifluoroborate using Pd(AcO)2/Cu(OAc)2/AcOH system. It was found that a variety of potassium aryltrifluoroborates selectively undergo the direct arylation across indoles and afford 2-aryl indoles in moderate to good yields. A broad range of functional groups were tolerated under the reaction condition, including CH3, OCH3, Cl, F, and CF3 groups. Both indole and N-substituted indole show good reactivity, and indoles and N-methyl indoles with CH3, OCH3, CN, and CO2CH3 substituents are able to be directly arylated with potassium phenyltrifuluorobotate. Compared to the reported catalytic system, this method utilized readily available air as oxidant without any ligands or the exclusion of moisture under mild reaction condition at room temperature.2. Pd(OAc)2 catalyzed ditect alkenylation of thiophenes and furansThiophenes and furans are important aromatic heterocycles that serve as key components of a variety of biologically active molecules and functional materials. The traditional alkenation of these heterocycles often involves the formylation and subsequent Wittig reactions. We studied the direct alkenylation of thiophenes and furans using Pd(OAc)2/AgOAc/DMF system. A variety of olefinic substrates such as acrylates, acrylamides and acrylonitrile can perform the direct alkenylation reactions with various thiophenes and furans to give the mono-alkenylated products in good yields. In most cases, the (E)-isomers were isolated as the major products; and the products could be alkenylated further to give disubstituted products.3. Pd(OAc)2 catalyzed homo-coupling of thiazoleThe bithiazole motif can be found in a number of molecules. These molecules are of biological activities and photovaltaic material qualities. The traditional synthesis of these compounds often involves the halidation and cross-coupling protocols or cyclization strategies. We found it efficient to synthesize bithiazole by homo-coupling in Pd(OAc)2/AgOAc/DMF system. Now, this work is ongoing.4. Pd(OAc)2 catalyzed induced dibromidation of 2-phenylprydineAryl halides are important substrates in coupling reactions. It is difficult to synthesize complex aryl halides, especially aryl dihalides. We used N,N-dibromo-4-methylbenzenesulfonamide as bromide reagent dibromided 2-phenylprydine. Now, this work is ongoing.