Doctor of Philosophy (PhD)
This dissertation entails design and development of two new synthetic methodologies made possible through the generation of cationic species, namely oxyallyl and amidoallyl cations. Chapter 1 involves literature survey on generation and trapping of oxyallyl cations. Mostly known for cycloaddition reactions with these elusive species, the most recent approach of direct nucleophilic capture of oxyallyl cations are discussed. Apt design of substrates and reaction conditions by Kartika Group to access a-electrophilic carbon towards the synthesis of a variety of value-added compounds, i.e., 1,4- and 1,6-dicarbonyls, carbazoles, densely substituted pyrroles and furans are elaborated.
Chapter 2 focuses on our discovery of a new type of reactivity of unsymmetrical oxyallyl cations generated by treating a,a-hydroxyalkynyl enol ethers with Py.TfOH. Our observation of the switch in regioselectivity when alkynes are substituted for their aliphatic counterpart to form α-bis aryl quaternary centers is presented. Detailed reaction optimization and scope of reaction, as well as synthetic utility of product is also elaborated.
Chapter 3 describes the classical and most recent methods of generation of nitrogen analogue of oxyallyl cations viz amidoallyl cations. This chapter details how the chemistry of 2-amino and 2-amidoallyl cations is developed over time, and their interceptions made possible through cycloadditions and direct trapping with nucleophiles. Ionization of α-hydroxy enamides with mild Brønsted acid and its capture at the α-carbon is discussed, which set the stage for Chapter 4. Chapter 4 is focused on our work on enantioselective b-functionalization of cyclic enamides made possible through strategic tautomerization of 2-amidoallyl cations to 1-amidoallyl cations with the help of chiral phosphoric acid catalyst. Optimization and scope of the reaction followed by a proposed mode of activation is discussed, supported by computational data.
Nepal, Binod, "New Synthetic Reactions Enabled by Protected Oxyallyl and Amidoallyl Cations" (2022). LSU Doctoral Dissertations. 5841.
Available for download on Sunday, May 21, 2023