A Bronsted Acid Catalyst for the Enantioselective Protonation Reaction

摘要

Metal-free chiral Br0nsted acid catalysis has been a growing area of research for the past decade. Several chiral Br0nsted acids such as urea/thiourea and TADDOL have been reported as an activator of electrophiles via hydrogen bonding. In 2004, the research groups of Akiyama and Terada independently reported a different type of activation of electrophiles by way of protonation with moderately strong phosphoric acids derived from chiral BINOLs. Following these seminal studies, it soon became clear that chiral phosphoric acids possessed tremendous potential for application in the development of novel asymmetric processes. However, due to the relatively low acidity of phosphoric acids, their utility has been limited to more basic nitrogen-based electrophiles such as imines or aziridines. The activation of aldehydes and ketones by chiral phosphoric acids has been very rare. Our group reported the first activation of carbonyl compounds with chiral phosphoric acids by introducing the 7V-trifluoromethane-sulfonyl (NTf) group into phosphoric acid.