Discovery and Mechanistic Insights of Main-Group Catalyzed C-H Functionalization Reactions of Dicoordinate Carbocations
Author: Brian Shao
Publisher:
Published: 2019
Total Pages: 240
ISBN-13:
DOWNLOAD EBOOKThis dissertation focuses on the discovery and developments of novel carbon-carbon (C-C) bond forming reactions through dicoordinate carbocation intermediates. Chapter one provides a brief introduction into the known reactivity of relevant aryl and vinyl carbocations. In particular, C-C bond forming transformations will be the main focus of this discussion. Our experimental work begins with the account of serendipitous discovery of intermolecular C-H insertion reactions of an aryl cation intermediate. We detail the reactivity-driven nature of our initial hypothesis and its development into a novel hydrocarbon arylation methodology. It was demonstrated that ortho-silylated aryl fluorides can be used as precursors for generating aryl cations capable of C-H insertion. The insertion chemistry exhibits inherent terminal selectivity in linear alkanes and is capable of activating one of the most challenges C-H bonds in methane. Subsequently, we followed the reactivity of our aryl cations to other dicoordinate carbocations as in vinyl cations. Utilizing a similar strategy hinged upon the use of silylium-weakly coordinating anion catalysis, vinyl cations were found to also undergo intermolecular insertion into sp3 C-H bonds. Here, we establish a reductive coupling process between vinyl triflates and various hydrocarbons. Extensive deuterium labeling studies also helped to uncover key features of the dicoordinate carbocation insertion mechanism. A detailed account of our hypotheses in establishing our mechanistic probe experiments is reported. In efforts to bring our new methodology to a more broadly applicable chemical space, we were determined to further develop our system for heteroatom compatibility. Our progress has culminated in a new mode of generation for vinyl cations under highly basic conditions, and results in the C-H insertion reactions in the presence of a wide variety of heteroatom-containing substrates. In these studies, 3-substitued cyclooctenyl vinyl triflates was a substrate class used to highlight the increased functional group tolerance of our new method. Utilization of lithium-weakly coordinating anions has allowed entry for our dicoordinate carbocation insertion chemistry into applications such as fine chemical syntheses.
