Enantio- and Diastereoselective Access to Distant Stereocenters Embedded within Tetrahydroxanthenes: Utilizingortho-Quinone Methides as Reactive Intermediates in Asymmetric Brønsted Acid Catalysis

Despite the tremendous advances of the past four decades, chemists are far from being able to use chiral catalysts to control the stereoselectivity of any desired reaction. New concepts for the construction and mode of operation of chiral catalysts have the potential to open up previously inaccessible reaction space. The recognition and categorization of distinct approaches seems to play a role in triggering rapid exploration of new territory. This Review both reflects on the origins as well as details a selection of the latest examples of an area that has advanced considerably within the past five years or so: the use of chiral anions in asymmetric catalysis. Defining reactions as involving chiral anions is a difficult task owing to uncertainties over the exact catalytic mechanisms. Nevertheless, we attempt to provide an overview of the breadth of reactions that could reasonably fall under this umbrella.