Theoretical Study on the Substituent and Ligand Effects in Gold-Catalyzed Organic Reactions
|Keywords||gold catalysis density functional theory alkyne ligandeffect reaction mechanism|
Over the past decade, the homogeneous gold catalysts have shownextremely high-efficient catalytic activity in organic synthesis. They playan important role in the construction of cyclic compounds. At the sametime, the density functional theory calculations are widely used inmetal-catalyzed organic reaction mechanism. In this dissertation, we havestudied the substituent and ligand effects in gold-catalyzed reactions bydensity functional theory calculations. The results are as following:1. In the study of the gold-catalyzed alkynyl indole cyclization, wefound that spiro intermediates are spontaneously formed from the indolereactants under the activation of the gold catalyst, followed by selective1,2-alkenyl migration or the attack of water molecules would formdifferent products. When the protecting group is an electron-donatinggroup,1,2-alkenyl migration is lower in activation energy; when theprotecting group is an electron-withdrawing group, the spiro intermediatecan be captured by water molecules in the system, which resulting incompletely different cyclization products.2. In the gold-catalyzed domino reaction of alkynes, anionic ligandscan control the reaction mechanism. The results showed that after thegold catalyzed cyclization of the alkynes, OMs-anion ligand, which has astronger basicity, can promote hydrogen shift. However, for the PF-6anion ligand, which is weaker in basicity, can not effectively assist thehydrogen migration. Instead, a trace amount of the water in the systemmay be the proton shuttle in these reactions. Therefore, the experimentaloutcomes are results from different basicity of the anionic ligand, thewater content, and other factors.