Photodriven Sm-Catalyzed Asymmetric Ketyl-Olefin Coupling

Area of Science:

• Organic Chemistry
• Catalysis
• Asymmetric Synthesis

Background:

• Samarium diiodide (SmI2) is a versatile single-electron reductant widely used in organic synthesis.
• While SmI2 has been utilized catalytically, enantioselective reductive cross-coupling reactions using catalytic SmI2 remain underexplored.

Purpose of the Study:

• To develop an enantioselective method for ketyl-olefin coupling mediated by catalytic samarium diiodide.
• To investigate the catalytic cycle and identify the active catalytic species in SmI2-mediated asymmetric reactions.

Main Methods:

• Enantioselective ketyl-olefin coupling reaction.
• Utilized a SmI2-derived catalyst in conjunction with a chiral pyridine-bis(oxazoline) (PyBOX) ligand.
• Employed a commercially available iridium (Ir) photocatalyst.
• Characterization through optical, electrochemical, and computational analyses.

Main Results:

• Successfully achieved an enantioselective ketyl-olefin coupling reaction using catalytic amounts of SmI2.
• Identified a samarium-stabilized PyBOX radical as the key reactive intermediate initiating the reductive coupling.
• Demonstrated a viable catalytic turnover strategy for SmI2 in asymmetric synthesis.

Conclusions:

• Developed the first known asymmetric method employing catalytic samarium diiodide for enantioselective reductive coupling.
• The findings pave the way for broader applications of SmI2 in catalytic asymmetric synthesis.
• The study elucidates the mechanism involving a novel Sm-stabilized radical species.