This dissertation focuses on the investigation of the formation of enantioenriched all-carbon quaternary stereocenters via the activation of alcoholderived electrophiles. Quaternary stereocenters are an abundant motif in natural products and bioactive molecules. Synthesizing them is challenging because they are sterically congested. Metal-catalyzed cross-coupling has revolutionized the way quaternary centers are formed by allowing substitution with carbon nucleophiles that otherwise do not undergo substitution with carbon electrophiles.
Chapter 1 describes the first stereospecific nickel-catalyzed crosscoupling of allylic pivalates with aryl boroxines to form allylic quaternary centers. This method allows access to highly enantioenriched allylic quaternary stereocenters equipped with highly versatile alkene handles that are not limited to terminal alkenes. Importantly, the allylic pivalate starting materials can be readily prepared in high enantiomeric excess which is crucial for the utility of this stereospecific process. In addition, this reaction proceeds via mild, functional group tolerant conditions.
Chapter 2 details a stereospecific Suzuki-Miyaura cross-coupling of allylic pivalates with vinyl boronic esters. The products of this reaction have divinyl quaternary centers that can be elaborated to allow access to enantioenriched quaternary centers remote from arenes. Both nickel- and palladium-based catalysts were examined in this reaction. Under nickel-catalyzed conditions, this reaction was found to be stereodivergent via solvent control. Thus, this work not only established a new route to highly enriched all-carbon quaternary stereocenters, it also elicits exciting mechanistic questions.
Chapter 3 focuses on the investigation of catalyst-controlled regioselectivity in the cross coupling of allylic pivalates with aryl boronic acids. Achieving catalyst control would overcome the need for biased substrates to control the regioselectivity. These studies form a foundation for the development of such a catalyst.
|Advisor:||Watson, Mary P.|
|Commitee:||Fox, Joseph M., Theopold, Klaus H., Silverberg, Lee J.|
|School:||University of Delaware|
|Department:||Chemistry and Biochemistry|
|School Location:||United States -- Delaware|
|Source:||DAI-B 82/4(E), Dissertation Abstracts International|
|Subjects:||Organic chemistry, Biochemistry, Molecular biology|
|Keywords:||Suzuki-Miyaura, Cross-couplings, Allylic pivalate, All-carbon, Quaternary stereocenters|
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