Date on Master's Thesis/Doctoral Dissertation
Hammond, Gerald B.
Yappert, M. Cecilia
Noble, Mark E.
Sunkara, Mahendra K.
The focus of my dissertation work is to study the gold-catalyzed intramolecular and intermolecular cyclizations involving oxonium intermediates towards the application of synthetically interesting frameworks under ambient conditions and developing a rational approach for the effective catalyst design in gold catalysis. We explored the goldcatalyzed oxygen-transfer reactions of 2-alkynyl-1,5-diketones or 2-alkynyl-5-ketoesters to furnish five-membered rings bearing a quaternary carbon tethered to a carbonyl group. The detailed mechanistic investigation on the newly proposed intramolecular [4+2] cycloaddition mechanism was performed by means of isotopic experiments and quantum chemical calculations. The reactivity of alkynylenolate was investigated in the reactions of allenic ketones and vinyl ketones which led to versatile syntheses of 2-alkynyl-1,5-diketones, 4-alkynyl-3-hydroxycyclohexones and 4-alkynylcyclohexenones. We also investigated the gold-catalyzed annulations of 2-alkynyl benzaldehyde with acyclic or cyclic vinyl ethers under very mild conditions, and successfully developed synthetically interesting dihydronaphthalenes, acetal-tethered isochromenes and bicyclo[2.2.2]octane derivatives often found in biologically active molecules and natural products. Although there have been numerous reviews and publications on new gold-catalyzed transformations, the development of new catalysts still relies on a hit-and-miss approach. Because the decay of the active cationic gold catalyst is the main reason for the high catalytic loading required for the majority of gold-catalyzed transformations, we developed a modular approach for effective catalyst design in gold catalysis. We discovered a new phosphine–based precatalyst that is broadly applicable and highly efficient—in the parts per million (ppm) range—at room temperature or slightly elevated temperatures (< 50 oC) . The ligand was preapared in one step from readily available starting materials.
Malhotra, Deepika, "Expanding the frontier of gold-catalyzed cyclizations and rational ligand design." (2014). Electronic Theses and Dissertations. Paper 893.