This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Radicals, atoms or molecules that readily react with other substances to form new bonds, are useful tools for building complex substances such as pharmaceuticals. But even when a radical is generated efficiently, the reaction cannot continue unless the catalyst returns to its original state.
A KAIST research team has developed a new strategy that balances radical generation and catalyst regeneration, broadening the possibility of using substrates that are difficult to activate to synthesize complex molecules needed for pharmaceuticals and other applications. The research team led by Professor Sarah Yunmi Lee of the Department of Chemistry developed a method that uses a ligand, a molecule that attaches to a metal catalyst and controls its properties, to effectively regulate the process by which a copper catalyst generates a radical and then returns to its original state. The work is published in the Journal of the American Chemical Society.
The team used a cyclopropenimine (CPI)-based ligand to tune the copper catalyst's redox behavior, helping it generate radicals and return to its active state. In this study, the team used tertiary alkyl halides, compounds in which bromine or chlorine is attached to a tertiary carbon center, as starting materials. When the copper catalyst breaks this bond, a highly reactive radical is generated.
This radical then forms a new carbon-carbon bond with another part of the same molecule, creating a ring-shaped structure. The process is similar to tying the two loose ends of a string together to form a loop. This is called a radical cyclization reaction.
When the team compared several types of ligands, they found that generating more radicals did not necessarily lead to more of the desired product. Some ligands were very effective at generating radicals but produced almost none of the final product. The best-performing CPI-based ligand, however, allowed radical generation and catalyst regeneration to proceed in balance.
If the catalyst is compared to a worker performing a task repeatedly, the CPI ligand acts as a helper that lets the worker move on to the next task without stopping after finishing one. As a result, the team synthesized 3,3-disubstituted oxindoles in high yields. These compounds have a ring framework relevant to medicinal chemistry and are used in pharmaceuticals and bioactive substances.
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