I. Enantioselective Alkynylation of Challenging, Biologically Relevant Tertiary Ether Stereocenters  II. Enantioselective Catalytic Alkynylation of Quinolones  III. Benzopyrylium Ions as Highly Tunable Organic Photocatalysts

Buivydas, Tadas

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I. Enantioselective Alkynylation of Challenging, Biologically Relevant Tertiary Ether Stereocenters II. Enantioselective Catalytic Alkynylation of Quinolones III. Benzopyrylium Ions as Highly Tunable Organic Photocatalysts

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Benzopyrylium ions are highly tunable electrophiles capable of participating in numerous reactions for the synthesis of biologically relevant compounds. Chapter 1 discusses the use of copper bis(oxazoline) ligand systems to control the enantioselective nucleophilic addition of copper acetylides to benzopyrylium ions to generate biologically relevant tertiary ether stereocenters. Density Functional Theory (DFT) studies indicated that the enantiodetermining step was governed by non-covalent interactions, such as pi-pi stacking. These reactions have implications for the synthesis of medicinally relevant tetrahydroxanthones such as phomoxanthone A (PXA). Chapter 2 discusses the first highly enantioselective copper bis(oxazoline) catalyzed alkynylation of quinolones via the facial selective dearomatization of in situ generated quinolinium triflates. DFT studies gave insight into the non-covalent interactions that governed enantiodetermining step with a simpler ligand system. The utility of this reaction was shown in the syntheses of various biologically relevant chiral N-heterocyclic alkaloids and 1,2 diamines. Finally, Chapter 3 demonstrates that benzopyrylium ions can also act as potent oxidizing photocatalysts to promote single electron transfer (SET) of feedstock chemicals such as toluene to provide benzylated chromenone products. These processes can be selectively controlled using a chiral phosphoric acid (CPA) catalyst. 2-Phenyl substituted benzopyrylium ions offer improved photocatalytic efficacy by avoiding self-reactivity, absorbing at higher wavelengths, and being highly tunable. A current family of newly developed 2-phenyl benzopyrylium ion photocatalysts demonstrates that reactions with toluene can be performed at various wavelengths of light, giving rise to the benzylated chromenone in high yields.

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