This thesis covers the development of new reaction methodologies for transformations of allenes and alkynes that are either Lewis base-catalyzed or where a Lewis basic functionality serves as a directing group. Chapter One is an introductory chapter, which reviews nucleophilic bifunctional Lewis base catalysis, a useful strategy for enhanced reactivity and selectivity in organocatalysis.
Chapter Two details the development of a stereoselective synthesis of tetrasubstituted allenes using a pyridylalanine-based peptide catalyst. Racemic allenes and N-acylimines were coupled together with diastereoselectivity of up to 42:1 and enantioselectivity of up to 94:6, successfully controlling two modes of stereoselectivity (point chirality and axial chirality) in the same molecule.
Chapter Three discusses mechanistic studies that were conducted to elucidate the reaction mechanism and mode of stereoinduction responsible for the high levels of stereoinduction observed for the coupling reaction. Data were consistent with a nucleophilic mechanism and suggested that the pyridyl peptide is a multifunctional catalyst.
Chapter Four details the discovery of an unprecedented annulation reaction of alkynes and α-keto esters catalyzed by tricyclohexylphosphine, resulting in highly substituted monocyclic and bicyclic cyclopentene derivatives. A hypothesis is also advanced for the formation these elaborate products from seemingly simple starting materials.
Chapter Five discusses the development of a substrate-directed regio- and stereoselective method for the synthesis of monofluoroalkenes. The Troc (2,2,2-trichloroethoxycarbonyl) carbamate group was found to be the best Lewis basic directing group, resulting in high yields and selectivity.
|Advisor:||Miller, Scott J.|
|School Location:||United States -- Connecticut|
|Source:||DAI-B 76/07(E), Dissertation Abstracts International|
|Keywords:||Alkynoates, Allenoates, Cycloaddition reactions, Enantioselectivity, Hydrofluorination, Phosphine catalysis|
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