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Date of Award
Hien M. Nguyen
Phenanthroline is a heterocyclic aromatic organic compound and commonly used in coordination chemistry acting as a bidentate ligand. The C-4 and C-7 of phenanthroline can often be substituted to change the binding capabilities of the ligand. Recently, there has been a push in the field of chemistry to create environmental-friendly chemical methodologies by utilizing catalysts and minimizing solvent. Herein, we have illustrated the C-4 and C-7 of phenanthroline can be tuned to develop an efficient and stereoselective catalyst for the formation of α-1,2-cis-fluorinated glycosides. By activating 2- deoxy-2-fluoro glycosyl halides with phenanthroline-based catalysts, we have been able to achieve glycosylations with high levels of α-selectivities and moderate to high yields. The catalytic system has been applied to several glycosyl halide electrophiles with a range of glycosyl nucleophilic acceptors. The proposed mechanism for this catalytic glycosylation system has been investigated by density functional theory calculations, indicating that the double SN2 displacement pathways with phenanthroline catalysts have lower barriers and ensure stereoselective formation of α-1,2-cis-2-fluoro glycosides. To further implement the concept of green chemistry we envisioned a method to combine the fluorination and glycosylation into one reaction. By substituting the sugar electrophile from glycosyl bromide to a glycal the amount of chemical waste is dramatically reduced. The direct fluorination and coupling of galactal with primary nucleophiles worked exceptionally well. By using stoichiometric excess (2 equiv.) of bathophenanthroline during the fluorination while coupling galactal and an alcohol nucleophile excellent stereoselectivity was achieved.
Dement, Paul, "Organocatalyzed Glycosylations Accessing 2-Deoxy-2-Fluoro Glycosides" (2021). Wayne State University Dissertations. 3566.