| Homogenous gold(I) catalysis has experienced an explosive growth over the past decade. The efficiency towards activation of alkyne, allene, and alkene renders cationic gold complexes unique in the organic synthesis. Despite the great progression, this area still suffers significantly from catalyst decomposition and low reactivity. In the past, our group introduced triazole-gold(I) complex (TA-Au) as a novel class of cationic gold complex with improved thermal stability and unique chemoselectivity. However, it was proved that TA-Au also showed lower reactivity. To overcome this paradox, compatible Lewis acid is used as the compatible additive for improving catalyst performance while maintaining enough stability. This thesis summarizes the development of this novel system and its application to various C-C, C-X bond formation reactions. Chapter 3 and 4 will discuss the initial discovery of a gallium triflate-assisted TA-Au catalysis in Nakamura reaction. This is the first time that the intermolecular Conia-ene (Nakamura reaction) is achieved and remarkably with catalyst loading as low as 100ppm. Chapter 4 and 5 also contains mechanistic investigation of Au/Ga system using various techniques including in situ IR, NMR, MassSpec. It is now clear that this Au/Ga system is in dynamic equilibrium and the role of Ga involves assisting dissociation of triazole ligand for substrate. Chapter 6 is extension of Nakamura reaction, based on which a cyclobutene synthesis is accomplished. Chapter 7 includes the efforts to develop a vinyl ether synthesis from cyclic 1,3-diketone and alkynes. Chapter 8 summarizes the synthesis of a-substituted vinyl sulfone, which is the first general synthesis in the literature. The Au/Ga system shows higher reactivity one more time. Chapter 9 focuses on the mechanistic aspect of TA-Au catalysis with 3,3-rearrangement of propargyl ester. Kinetics experiments show that the rate has first-order dependence on substrate and TA-Au catalyst. Variable temperature experiment determines activation parameter and with TA-Au derivatives Hammett plot is also established. With these results, the associative ligand exchange of substrate with TA-Au is determined as the turnover-limiting step. |
