Organocatalytic, Michael-Stetter reaction and rhodium(I)-catalyzed hydroheteroarylation of acrylates with benzoxazoles: reaction development and investigations into origins of enantioselectivity
Date
2015
Authors
Filloux, Claire M., author
Rovis, Tomislav, advisor
McNaughton, Brian R., committee member
Prieto, Amy L., committee member
Crans, Debbie C., committee member
Hentges, Shane T., committee member
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Abstract
The chapters that follow describe two independent investigations. Both relay the development of experimental methods for the catalytic, asymmetric addition of carbon-hydrogen bonds to alkenes. In the first chapter, nucleophilic amine and N-heterocyclic carbene cocatalysts cooperate in the organocatalytic, cascade synthesis of benzofuranone products in good yields and high enantioselectivities. Importantly, the cascade protocol is found to outperform a two-pot procedure in which reaction intermediates are isolated and purified before the second step. Mechanistic studies reveal that additives and geometry of an olefin intermediate crucially influence reaction enantioselectivity. In the second method, a bulky Rh(I)-bisphosphine complex catalyzes the asymmetric, intermolecular addition of benzoxazoles to methacrylate derivatives in fair to excellent yields and good to excellent enantioselectivities. Detailed deuterium labeling and epimerization studies provide considerable insight into the reaction mechanism: C-H activation is reversible; migratory insertion is likely enantiodetermining; and the bulky- bisphosphine ligand likely boosts reactivity and selectivity by discouraging deleterious ligation of benzoxazole starting materials to on- or off-cycle rhodium complexes and by impeding coordination-induced product epimerization.
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Subject
catalysis
organic
asymmetric
rhodium
N-heterocyclic carbene