Doctor of Philosophy (PhD)
The focus of this dissertation is the development of a C-H functionalization method using redox catalysis and the synthesis of saccharides using thioglycosides. Chapter 1 is a review of C-H functionalization and visible-light photoredox catalysis. Over the years there have been many significant contributions to the field of C-H functionalization. Select examples have been discussed and a foundation for the method developed in chapter 2 has been outlined. Chapter 2 discusses the development and optimization of a C-H functionalization method. This approach uses the Tzo directing group and Ir(ppy)3 to activate a remote C-H bond via 1,6- and 1,7-radical translocation. It was confirmed that this method required acid and Ir(ppy)3 to afford decent yields of the hydroxylated products. An array of sulfonamides and sulfonate esters were screened in efforts to expand the substrate scope.
Chapter 3 provides an overview of chemical O-glycosylation. Stereoselective synthesis of oligosaccharides has been a challenge that many researchers have made attempts to address over the years. Select examples of glycosylation methods have been discussed along with the benefits and shortcomings. In chapter 4, a mild, metal-free method for glycosylation with thioglycosides is established and optimized. Thioglycosides are frequently employed in glycosylations due to their chemical stability, however, the harsh/toxic conditions necessary to activate them is a major downfall. To address this concern, 4-aryl-3-butenylthioglycosides were activated using visible-light in the presence of Umemoto’s reagent. A putative EDA complex forms and initiates departure of the leaving group. Changing the light source from blue LEDs to violet LEDs, improved the reaction time (24 hours to 2 hours) without compromising yield. Observations made during these experiments paved the way for the method developed in Chapter 5.
Chapter 5 outlines an acid-promoted glycosylation of 4-aryl-3-butenylthioglycosides. In an effort to combine the stability of thioglycosides with the reactivity of trichloroacetimidates, activation of 4-aryl-3-butenylthioglycosides was demonstrated with 10 mol% of triflic acid (or TMSOTf). Glycosidic linkages were formed within in good to excellent yields and stereoselectivity can be achieved by neighboring group participation. 4-Aryl-3-butenylthioglycosides exhibit low reactivity at -20oC and this latency will ultimately be exploited in the synthesis of a trisaccharide.
Deveaux, Kristina, "Development of Remote Hydroxylation via Redox Catalysis and Mild Activation of Thioglycosides for O-Glycosylation" (2017). LSU Doctoral Dissertations. 4167.