Tehshik Yoon

Stereocontrol in Photochemical Reactions

Control over the stereochemistry of photochemical reactions, particularly using enantioselective catalysts, has been a long-standing challenging synthetic problem with few general solutions. It has commonly been argued that the high-energy intermediates involved in photochemical transformations limit the opportunities for effective stereocontrol. We disagree with this assessment, and recently developed a method for highly enantioselective [2+2] photocycloaddition reactions using a combination of chiral Lewis acid and transition metal photocatalysis. This dual catalyst approach offers a robust strategy to control the reactivity of a wide range of reactive intermediates that can easily be generated using photoredox catalysis. Key to the success of this strategy is the ability to independently tune the chiral environment of the Lewis acid without interfering with the photochemical properties of the light-absorbing chromophore.