Enantioselective cyclizations and cyclization cascades of samarium ketyl radicals

The rapid generation of molecular complexity from simple starting materials is a key challenge in synthetic science. Enantioselective radical cyclization cascades have the potential to deliver complex, densely-packed, polycyclic architectures, with control of three dimensional shape, in one-step. Unfortunately, carrying out reactions with radicals in an enantiocontrolled fashion remains challenging due to their high reactivity. This is particularly the case for reactions of radicals generated using the classical reagent, SmI2. Here, we demonstrate that the first enantioselective SmI2-mediated radical cyclizations and cascades can convert symmetrical ketoesters to complex carbocyclic products bearing multiple stereocenters with high enantio- and diastereocontrol, and exploit a simple, recyclable chiral ligand. The first computational study of a SmI2-mediated carbon-carbon bond-forming process has been used to probe the origin of the selectivity. Our studies suggest that many processes that rely on SmI2 can be rendered enantioselective by the design of suitable ligands.