Dynamic Kinetic Asymmetric Transformation of Racemic Diastereomers: Diastereo‐ and Enantioconvergent Michael–Henry Reactions to Afford Spirooxindoles Bearing Furan‐Fused Rings

Amines as Catalysts: Dynamic Features and Kinetic Control of Catalytic Asymmetric Chemical Transformations to Form C-C Bonds and Complex Molecules

Carbonyl transformations involving enolates and/or enamines have been used for various types of bond-forming reactions. In this account, catalysts and catalyst systems that have amino acids or primary, secondary, and/or tertiary amines as key catalytic functional groups that we have developed to accelerate chemical transformations, including regio-, diastereo- and enantioselective reactions, are discussed. Our chemical transformation strategies and methods that use amine derivatives as catalysts are also discussed. As amines can have different functions depending on protonation and on the species formed during the catalysis (such as enamines and iminium ions), dynamics and kinetic controls are the keys for understanding the catalysis. Further, strategies that harness dynamic steps and kinetic control in amine-catalyzed reactions have enabled the synthesis of complex molecules in stereocontrolled manners. Understanding the dynamic features and the kinetic controls of the catalysis will further the design of the catalysts and the development of chemical transformation strategies and methods.

Rearrangement-Driven Molecular Diversity: Synthesis of Functionalized Pyrones, Orthoesters, and Xanthones from Spiroketals

The reaction of tricyclic 5,5-benzannulated spiroketals with trifluoroacetic acid (TFA) and AlCl₃ furnished benzopyranobenzopyrans, benzofuro-orthoesters, and benzofuroxanthones. Whereas the reaction of tricyclic 5,5-benzannulated spiroketals with TFA produced the pyrones, the reaction with AlCl₃ furnished densely functionalized orthoesters and xanthones. The formation of these products was rationalized by fascinating mechanistic pathways involving semipinacol/α-ketol molecular rearrangements.