Catalytic Asymmetric Aza-Diels–Alder Reactions: The Povarov Cycloaddition Reaction

The Povarov reaction provides a straightforward and modular entry to 1,2,3,4-tetrahydroquinolines (THQs). Despite its importance, it was only very recently that several highly efficient catalytic asymmetric protocols for this reaction have been developed, as summarized in this review which falls on the 50^th anniversary of Povarov's pioneering disclosure. Furthermore, this review collects and critically discusses the interrupted versions of the reaction, often featuring intriguing and still unclear mechanicistic pathways. 1 Introduction 2 Catalytic Asymmetric Povarov Cycloaddition Reactions 2.1 Chiral Lewis Acid Catalysis 2.2 Chiral Brønsted Acid Catalysis 2.2.1 Chiral Phosphoric Acid Catalyzed Povarov Cycloaddition Reactions 2.2.2 Chiral Urea Catalyzed Povarov Cycloaddition Reactions 3 Catalytic Asymmetric Interrupted Povarov Reactions 3.1 Intermolecularly Interrupted Povarov Reactions 3.2 Intramolecularly Interrupted Povarov Reactions 3.2.1 Interrupted Povarov Reactions with Salicyaldehyde-Derived Imines 3.2.2 Interrupted Povarov Reactions with Glyoxylic Acid Derived Imines 4 Conclusion