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Fang, Jian

Chemistry

2020

Ph. D.

[Beta]-hydroxy-[alpha]-diazo carbonyl compounds have been shown to display diverse reactivity profiles that can lead to a variety of useful products. This specific combination of functional groups can react in several mechanistically distinct ways depending on the presence or absences of other groups within the molecule. For example, [gamma]-silyloxy-[Beta]-hydroxy-[alpha]-diazo carbonyls react with Lewis acids via fragmentation reactions to generate tethered aldehyde ynoate or ynone products. A portion of this thesis describes how this methodology was applied toward the synthesis of an important bioactive natural product: aspidospermidine. [Beta]-Hydroxy-[alpha]-diazo carbonyls are also convenient precursors to vinyl cations. The vinyl cation is generated by loss of N2 gas from a vinyl diazonium intermediate, which is formed by the dehydroxylation of a [Beta]-hydroxy-[alpha]-diazo carbonyl compound. A portion of this thesis investigated the intramolecular reaction between vinyl cations and aromatic rings to form tricyclic indenones and naphthanols. Importantly, this research has also shown that the vinyl diazonium intermediates are themselves a strong electrophilic intermediate that can react with nucleophiles in conjugate addition reactions. These reactions occur faster than loss of N2. More specifically, this thesis describes our finding that vinyl diazonium ions can be trapped by indole derivatives to provide all-carbon quaternary centers in high yield. This reaction provides a novel method to prepare structurally complex products that contain a diazo functional group that can be taken advantage of in subsequent synthetic transformations.