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Abstract

The thesis is focused on 1,10-phenanthroline (phen)-assisted homogeneous oxidative gold catalysis using hydrogen peroxide (H2O2) as oxidant. It is an unprecedented oxidative gold catalysis strategy with an ideal “benefit balance”, not just as a more attractive substitute of common methodologies, but as an extraordinary reaction system. The efficient constructions of 3-alkynylbenzofurans, 1,3-diynes and polyynes were possible by this catalytic system (Au/phen/H2O2). The thesis considers the significant advantages (ideal “benefit balance”) and challenges (no-report) of H2O2 as an oxidant for oxidative gold catalysis. In the first part (Chapter 2), we focused on exploring the possibility of oxidative gold catalysis using H2O2 as oxidant and the potential application value of this reaction system. We discovered that bidentate N-ligands (phen) can effectively promote the oxidation of AuI to AuIII in the presence of H2O2. Furthermore, a set of experiments with stoichiometric gold(I) complexes demonstrated that this catalytic system can be applied for homogeneous gold-catalyzed C(sp2)-C(sp) and C(sp)-C(sp) cross-coupling reactions. The gold-catalyzed cyclization-functionalization is a powerful approach to construct high-value organic molecules. However, current strategies mainly rely on expensive external oxidants or pre-functionalized substrates, which exhibit low atom economy and high costs. To circumvent these drawbacks, in the second part (Chapter 3), we focused on investigating the use of this catalytic system for efficient gold-catalyzed cyclization-functionalizations. A direct construction of 3-alkynylbenzofurans from terminal alkynes was possible by this gold-catalyzed process. Green and inexpensive oxidants, simple gold catalysts, mild reaction conditions, high atom economy, remarkable selectivity, wide substrate scope, broad functional group compatibility and a facile gram-scale synthesis make this alkynylative cyclization method practical for many forms of cyclization reactions. In contrast to prior methods neither pre-functionalized alkynes nor expensive external oxidants are needed. Conjugated 1,3-diynes are unique carbon frameworks which are widely found in natural products, biologically active molecules and functional materials. Considering the importance of synthetic methods for conjugated diynes, especially unsymmetrical 1,3-diynes, we next focused on investigating the use of this catalytic system for a gold-catalyzed cross-coupling of terminal alkynes. An efficient synthesis of unnsymmetrical 1,3-diynes from terminal alkynes via this new gold catalytic system was developed (Chapter 4). A wide range of substrates, including several complex molecules and marketed drugs, were transferred with excellent functional group tolerance. Furthermore, the catalyst system was applied at a gram scale and an extension towards the synthesis of polyynes via a relay strategy was possible. Considering the importance of polyynes in chemical and materials research, and tedious synthesis procedure of the current strategy. In the fourth part (Chapter 5), we focused on exploring gold-catalyzed C(sp)–C(sp) cross-coupling of alkynylsilanes using H2O2 as oxidant. Through this catalytic system, 1,3-diynes and polyynes can be successfully prepared from ethynyltrimethylsilanes without pre-functionalization or deprotection. Compared with current synthetic strategies towards polyynes, our method greatly improves the synthetic efficiency, provide new ideas for the synthesis of polyynes.