Doctor of Philosophy
Flowers, Robert A.
Other advisers/committee members
Foster, Natalie; Heindel, Ned; Wernett, Patrick
Samarium diiodide (SmI2) was first introduced to synthetic chemists in 1980. Although initially considered an esoteric compound, SmI2 is now a standard reductant in organic laboratories and its use in synthesis is featured in nearly 100 publications a year. The unique place held by SmI2 in the arsenal of synthetic chemists is a result of its versatility in mediating numerous, fundamentally important reactions in organic synthesis including reductions, reductive couplings, and cascade reactions. While numerous reactions have been developed for SmI2, its scope in synthesis has not been fully realized as new applications for this reagent are steadily being discovered.One of the intriguing features of SmI2 is that the addition of cosolvents or additives can be used to control the chemo- and diastereoselectivity of reactions. In fact, nearly all synthetic procedures utilize additives that are critical for the success of reactions initiated by SmI2. Additives commonly utilized to alter reactions of SmI2 are typically classified into three major groups: (1) Lewis bases, including HMPA and other electron donor ligands and chelating ethers, (2) proton sources (predominantly water and alcohols), and (3) inorganic additives (NiI2, FeCl3, etc.). The research presented in this defense focuses on studying well-established SmI2-additive systems to gain mechanistic information on the role of the additive in SmI2 reactions. Within the systems studies we determined: (a) relative rates of reduction between α,β-unsaturated esters and aldehydes, (b) the dual role of HMPA as a cosolvent in the samarium Barbier reaction, (c) the change in the reaction pathway when catalytic amounts of Ni(II) salts are added to SmI2 reactions, (d) the impact of H2O added to the Sm-mediated ring opening reduction of lactones, and (e) the mechanism of action of the powerful Sm-H2O-amine additive system in the unprecedented reduction of esters. The systematic study of SmI2-additive systems has led to a deeper understanding of the chemistry of SmI2 reagent systems, providing a profound impact on their applications in organic synthesis and the development of general approaches to making the chemistry of SmI2 more efficient.
Choquette, Kimberly Ann, "Mechanistic Studies on the Effect of Additives in SmI2-Mediated Reactions" (2013). Theses and Dissertations. 1457.