Chiral phosphoric acids as versatile catalysts for enantioselective transformations

Chiral phosphoric acids derived from axially chiral biaryls and related chiral Brønsted acids have emerged as an attractive and widely applicable class of enantioselective organocatalysts for a variety of organic transformations. This review focuses on recent achievements in the development of enantioselective transformations using these axially chiral phosphoric acids and their analogues as chiral Brønsted acid catalysts. The contents are arranged according to the specific types of carbon-carbon bond-forming reactions, followed by carbon-heteroatom bond-forming reactions and functional group transformations, including reduction and oxidation. Further applications to combined phosphoric acid and metal complex catalytic systems and new aspects in the development of chiral Brønsted acid catalysts are also highlighted. 1 Introduction 2 Chiral Phosphoric Acids as Enantioselective Brønsted Acid Catalysts 3 Mannich and Related Reactions 4 One-Carbon Homologation Reactions via Activation of Imines 5 Friedel-Crafts and Related Reactions 6 Ene (Type) Reactions 7 Cycloaddition Reactions 8 Cyclization Reactions 9 Transformations via Protonation of Electron-Rich Double Bonds 10 Miscellaneous Carbon-Carbon Bond-Forming Reactions 11 Carbon-Heteroatom Bond-Forming Reactions 12 Transfer Hydrogenation Reactions 13 Oxidations 14 Combined Use of Metal Complex and Phosphoric Acid Catalysts 15 New Aspects in the Development of Chiral Brønsted Acid Catalysts 16 Conclusions.