Ligand design in gold catalysis and chemistry of gold-oxonium intermediates.

Gold catalysis is considered one of the most important breakthroughs in organic synthesis during the last decade. Many gold-catalyzed reactions suffer from high catalyst loading, which is a serious limitation on the application of gold catalysis in larger scale synthesis. Because ligands play a major role in the tuning of reactivity of transition metal catalysts, there has been an increased effort on rationally understanding ligand effects in gold catalysis and using a rational ligand design to achieve higher efficiency. In the first part of this chapter, selected examples of ligand design in gold catalysis are discussed. In the second part, the chemistry of gold-oxonium intermediate is examined. An oxonium intermediate is generated when a oxygen nucleophile (ketone, aldehyde, or ether) attacks a cationic gold-activated multiple bond. This oxonium intermediate, being a highly energetic species, has the potential to undergo further transformations such as electron transfer/rearrangement/protodeauration to form diverse products.