"Mechanistic Studies of Samarium(II) Mediated Reductions"
Samarium diiodide (SmI₂) is a powerful single electron reducing agent that drives many important reactions in organic synthesis, yet there are still several mechanistic questions that remain poorly understood. Specifically, the mechanism of SmI2-promoted carbonyl-activated alkene couplings is still debated and the impact of solvent on rate and mechanism of reduction remains unclear. To address these questions, synthetic experiments were combined with kinetic measurements that have the ability to monitor reactions on the millisecond timescale using stopped-flow spectrophotometry. Results demonstrate that coupling mechanisms of carbonyls with activated alkenes cannot be generalized, because they are influenced by the electronic properties of the substrate and the steric environment adjacent to the reacting functional group. In addition, the work demonstrates that solvent coordination to SmI2 plays a major role on influencing the rate and mechanism of substrate reduction. These new insights will guide the design of new reactions that could be useful in the design of new pharmaceuticals.