Stereoselective addition of terminal alkynes to oxocarbenium and iminium ions

Date
2016
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University of Delaware
Abstract
This dissertation focuses on investigations of stereoselective additions of terminal alkynes to oxocarbenium and iminium ions. Chapter 1 describes the development of mild reaction conditions for the addition of unfunctionalized, terminal alkynes to a-halo oxocarbenium ions, formed in situ from acetal precursors. When coupled with bromination to form a β-halo acetal intermediate, this method enables the preparation of difunctionalized oxygen heterocycles from simple enol ether precursors in excellent diastereoselectivities. ☐ Chapter 2 describes our studies towards the development of alkynylation conditions to make C-glycoside. This reaction provides alkynylated 2-deoxy sugars in synthetically useful yield and excellent diastereoselectivity. The alkynylation utilizes an unfunctionalized alkyne and readily available protected sugar substrates. ☐ Chapter 3 focuses on the development of a copper-catalyzed alkynylation of 1-aryl isoquinolinium ions that delivers cyclic α-diaryl tetrasubstituted amines in good yields and high enantioselectivities. This reaction employs a catalyst with commercially available components, and tolerate a wide range of isoquinolines and alkynes. Mechanistic studies suggest an aggregated Cu/Ph-PyBox complex may act as the active catalyst. ☐ Overall, this dissertation describes my efforts towards developing methodology for the selective addition of terminal alkynes to reactive cationic intermediates, including oxocarbenium ions and iminium ions.
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