Collections > Electronic Theses and Dissertations > Activation of Carbodicarbene Catalysts for Diene Hydrofunctionalization and Exploration of Chemical Reactivity Using Commodity Chemicals
pdf
Available after 13 June, 2020

I. Lewis Acid Activation of Carbodicarbene Catalysts for Rh-Catalyzed Hydroarylation of Dienes The activation of carbodicarbene (CDC)−Rh(I) pincer complexes by secondary binding of metal salts is reported for the catalytic site-selective hydroarylation of 1,3-dienes. The reactions are promoted by 5 mol % of a readily available tridentate (CDC)−Rh complex in the presence of an inexpensive lithium salt. A variety of terminal and internal dienes were tolerated under the reaction conditions, as well as ester, alkyl halide, and boronate ester functional groups. X-ray crystallographic data and mechanistic experiments provide support for the role of the metal salts on catalyst activation and shed light on the reaction mechanism. The increased efficiency (120 to 22 °C) made available by catalytic amounts of metal salts to catalysts containing C(0) donors is a significant aspect of the disclosed studies. II. Synthesis and Desymmetrization of Fully Substituted, Meso-Fused Systems Derived from Benzene Oxide Ozonolysis of the Diels–Alder adducts derived from benzene oxides and N-alkylmaleimides resulted in fully-substituted, meso-bicyclic systems bearing six contiguous stereocenters, isolated as diols upon reductive workup with NaBH4. Variation in the workup allowed for isolation of two different diastereomers, through double epimerization of the imide stereocenters. Detailed study of each component of the workup revealed that the unexpected diastereomer arose from epimerization of the product through the action of in situ-generated base, rather than a retro-Diels–Alder/recombination sequence during the ozonolysis. These meso-diols were transformed in high yields to enantioenriched desymmetrized products via asymmetric nucleophilic epoxide opening and acylation reactions, providing a strategy for obtaining highly-substituted, enantioenriched fused rings through desymmetrization. III. Hydroxylamine as a Precursor for Nitrene and Diimide Formation: C−C Bond Aziridination and Reduction Hydroxylamine is used as a precursor for metal-nitrenoids and diimide. The first part of this chapter covers the initial discovery that hydroxylamine can be used for the aziridination of alkenes in the presence of CO2, a protecting group, and a rhodium catalyst. The reactivity remains unoptimized, despite significant efforts. During these studies, the reduction of alkenes under similar conditions was observed. The second part of this chapter discusses the in situ formation of diimide with the use of hydroxylamine and a protecting group. An initial substrate scope is presented, although some challenges remain. Terminal olefins are reduced in high yields, whereas internal olefins are less reactive. The reduction of terminal alkynes is also possible, albeit in lower yields. Further studies should reveal the mechanism of the reaction and should provide optimize conditions for the less reactive substrates.