Enantioselective cyclizations and cyclization cascades of samarium ketyl radicals
Journal: Nature Chemistry
Publication Date: 07 August, 2017
Department of: Chemistry
Breakthrough in the control of important radical reactions
Enantioselective synthesis allows the 3D molecular architectures of society’s drugs, agrochemicals and materials to be assembled. Many of the complex molecules we need also contain intricately linked rings of atoms and the rapid and selective generation of these structures is a major challenge. Domino sequences of ring-forming reactions involving radical intermediates could provide a breakthrough. Although there are many reagents that generate radicals, samarium diiodide (SmI2) is one of the most effective and is used worldwide. Unfortunately, carrying out reactions with radicals in enantioselective fashion remains challenging due to their high reactivity.
Forty years since the introduction of SmI2 as a reagent for synthesis, and thousands of publications later, the first use of a chiral ligand to control the selectivity of reactions using the reagent has been achieved thus allowing vital molecules to be made quickly and efficiently. Researchers at the University of Manchester have invented enantioselective radical cyclization reactions that exploit SmI2 and a recyclable chiral ligand and convert simple feedstocks to complex polycyclic products with exquisite control of 3D shape. The study suggests that many synthetic processes that rely on SmI2 can now be used for the enantioselective synthesis of society’s most important molecules and materials.
- SmI2 is a commercially available reagent used routinely in synthetic chemistry around the world.
- Radicals are reactive intermediates bearing unpaired electrons.
- A chiral ligand can exist in left and right handed forms, or enantiomers.
- When a chiral ligand is used in just one enantiomeric form, it can control the formation of a chiral product so that only one enantiomer results (enantioselective).