Light empowers contra-thermodynamic stereochemical editing

Creating, preserving, and manipulating the stereochemistry of organic compounds has long been a cornerstone of modern organic synthetic chemistry, and the synthetic routes are typically designed according to stereoselectivity-determining step that is known as stereochemical logic. As an alternative strategic platform, stereochemical editing, wherein the chiral- or geometry-defining events are decupled from the main scaffold or complexity-forming steps, has the potential for late-stage flexibility in generating isomers from a single compound. However, under many instances, the desired stereochemical editing processes are contra-thermodynamic on ground states and thus unfavorable. Recent research has begun to leverage photocatalysis to yield many potentially generalizable concepts to empower contra-thermodynamic stereochemical editing by providing approach to irreversible elementary steps via excited electronic states and/or by introducing thermochemical biases. A broad range of synthetically valuable contra-thermodynamic stereochemical editing processes were thus invented, including deracemization of racemic chiral molecules, positional alkene isomerization, and dynamic epimerization of sugars and diols. In this review, we highlight how an understanding of the mechanisms of visible-light photocatalysis and of the general reactivity patterns of the photogenerated radical intermediates has been engineered to develop these concepts.