Browsing by Author "Bandar, Jeffrey, committee member"
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Item Open Access Development of N-aryl phenoxazines as strongly reducing organic photoredox catalysts(Colorado State University. Libraries, 2020) McCarthy, Blaine Gould, author; Miyake, Garret, advisor; Bandar, Jeffrey, committee member; Krummel, Amber, committee member; James, Susan, committee memberN-aryl phenoxazines were identified as a new family of organic photoredox catalysts capable of effecting single electron transfer reductions from the photoexcited state. A number of phenoxazines bearing different N-aryl and core substituents were synthesized, characterized, and employed as catalysts. Spectroscopic and electrochemical characterization of these phenoxazines was used to establish structure-property relationships for the design of visible-light absorbing, strongly reducing organic photoredox catalysts. The application of phenoxazines as catalysts for organocatalyzed atom transfer radical polymerization (O-ATRP), a light-driven method for the synthesis of well-defined polymers, revealed the importance of several catalyst properties for achieving control over the polymerization. Investigation of the properties and catalytic performance of N-aryl phenoxazines has provided fundamental insight into the reactivity of organic excited state reductants and photophysical properties of organic molecules. The catalysts developed through this work provide sustainable alternatives to more commonly used precious-metal containing photoredox catalysts.Item Open Access Expanding the medicinal chemistry toolbox: development of new pyridine and piperidine functionalization strategies(Colorado State University. Libraries, 2022) Greenwood, Jacob W., author; McNally, Andrew, advisor; Bandar, Jeffrey, committee member; Sambur, Justin, committee member; Chatterjee, Delphi, committee memberNitrogen-containing heterocycles, such as pyridine, are ubiquitous in pharmaceuticals, agrochemicals, ligands, and materials. Therefore, robust methods for their direct functionalization are highly desired. Chapter one focuses on the importance of pyridine-containing molecules, the reactivity of pyridine, and challenges associated with functionalization of such compounds. In chapter two, a method for bipyridine synthesis is discussed that uses pyridylphosphonium salts as radical precursors. Other radical precursors failed to provide the desired products, highlighting the unique reactivity imparted by the phosphonium group. In chapter three, pyridylphosphonium salts are explored as alternatives to cyanopyridines in photoredox-catalyzed radical coupling reactions. This work expands the scope of the reaction manifold to complex pyridine substrates where installation of the cyano group can be challenging. Chapter four introduces the value of piperidines and challenges associated with their synthesis. A strategy is described to address these limitations using isolable, cyclic iminium salts as a general platform to elaborate the piperidine scaffold with several medicinally relevant functional groups. An alternative piperidine synthesis is presented in chapter five, where the mild transformation of a range of pyridines into pyridinium salts is achieved, followed by mild hydrogenation to the desired piperidine products. This method operates under mild conditions and can tolerate substitution at the 2-position of the pyridine substrate. As a result, a large amount of pyridine starting materials can now be engaged to form piperidines that are challenging to make with other technologies.Item Open Access New methods to access functionalized N-heterocycles(Colorado State University. Libraries, 2021) Patel, Chirag, author; McNally, Andrew, advisor; Bandar, Jeffrey, committee member; Reynolds, Melissa, committee member; Kipper, Matthew, committee memberN-heterocycles are ubiquitous in pharmaceuticals and agrochemicals. Their prevalence is due to the unique properties they can impart to a molecule. Due to their ubiquity, it is vital that synthetic chemists be able to modify the structure of these valuable scaffolds. Despite a great deal of literature on the functionalization of these important motifs, challenges toward the functionalization of N-heterocycles remain. Chapter 1 will highlight the importance of azaarenes in pharmaceuticals and explain the properties that make these structures so prevalent in drugs. Classical and modern methods to functionalize pyridines and diazines will also be discussed. Chapter 2 will describe the development of the phosphonium salt chemistry in the McNally lab and the use of these reactive intermediates to aminate pyridines and diazines via the Staudinger reaction. Chapter 3 will introduce the concept of phosphorus ligand-coupling and briefly describe its previous application toward the synthesis of bis-heterobiaryls. This chapter will also cover the importance of fluoroalkyl groups in both the pharmaceutical and agrochemical industries. Current methods to fluoroalkylate azaarenes will be discussed, and the development of a novel fluoroalkylation strategy via a phosphorus ligand-coupling reaction will be explained. Finally, chapter 4 covers ongoing research into the synthesis of N-alkyl/aryl pyridiniums and their hydrogenation to N-substituted piperidines. The importance of N-substituted piperidines and the limitations to their synthesis are described.Item Open Access Selective halogenation of pyridines and diazines via unconventional intermediates(Colorado State University. Libraries, 2022) Levy, Jeffrey N., author; McNally, Andrew, advisor; Bandar, Jeffrey, committee member; Neilson, Jamie, committee member; Hansen, Jeffrey, committee memberPyridines and diazines are prevalent in pharmaceuticals, agrochemicals, ligands, and other organic materials, and it's vital that synthetic chemists can selectively functionalize these heterocycles. We have shown that heterocyclic phosphonium salts and Zincke imine intermediates can be used to regioselectively functionalize pyridine rings. This dissertation describes the development of these strategies with an emphasis on new approaches to selectively halogenate pyridines, which we view as a long-standing challenge in organic chemistry. Chapter One introduces the importance of pyridines and diazines, as well as established methods and limitations in halogenating these azines. Chapter Two provides an overview of the synthesis and reactivity of heterocyclic phosphonium salts, and then describes a new strategy to access 4-halogenated pyridines via these reagents. Chapter Three examines further developments of heterocyclic phosphonium salts, including as how they can be used to selectively add amines and fluoroalkyl substituents to pyridines. Chapter Four provides an overview of pyridine ring-opening reactions and then shows how this approach can be applied to selectively halogenate the 3-position of pyridines. Chapter Five describes how modifications to the ring-opening strategy can be used to change halogenation site-selectivity. This chapter also shows that the ring-opened intermediates can be used to form isotopically labeled pyridines and aniline derivatives.Item Open Access The total synthesis of the baulamycins(Colorado State University. Libraries, 2019) Thielman, Jonathan Rhines, author; Williams, Robert M., advisor; Bandar, Jeffrey, committee member; Finke, Richard, committee member; Slayden, Richard, committee memberDescribed herein are the total syntheses of the antibiotic polyketides baulamycin A and baulamycin B. A synthesis giving rise to much of the baulamycins' initially-proposed structures is also described.Item Open Access Understanding selectivity in organic reactions through density functional theory(Colorado State University. Libraries, 2024) de Lescure, Louis Raymond Philibert, author; Paton, Robert, advisor; McNally, Andrew, advisor; Bandar, Jeffrey, committee member; Kennan, Alan, committee member; Herrera-Alonso, Margarita, committee memberThe success of chemical reactions is often expressed through the lens of selectivity, defined as the preference for a desired reaction pathway over an undesirable one. A profound understanding of the rationale behind the selectivity of chemical reactions is crucial for the progression of synthetic methodologies in organic chemistry. Utilizing quantum chemical approximations, density functional theory (DFT) calculations offer unparalleled insights into the electronic structures and mechanisms of reactions, which can be correlated with observed empirical selectivities. This dissertation demonstrates the significant utility of DFT, in tandem with experimental evidence, in elucidating the intricate mechanisms of reactions. Chapter 1 defines the thematic and methods used throughout this thesis. Chapters 2 and 3 detail collaborative work with the McNally group at Colorado State University. Here, we developed innovative methods for the halogenation of pyridines and advanced modifications of pyrimidine rings utilizing redesigned Zincke chemistry. This chapter focuses on the factors influencing the regioselectivity of halogenation processes and provides mechanistic insights into the formation of crucial intermediates. Chapter 3 outlines a joint project with the Race group at the University of Minnesota, where we explored the homologation of benzylic carbon-bromide bonds. Our investigations centered on the ring-opening of phenonium intermediates, a critical step in determining the success of the reaction. Chapter 4 presents a collaboration with the Aggarwal group at the University of Bristol. This chapter examines the nuanced interplay between kinetic and thermodynamic factors that govern the enantioselectivity of the reaction discussed. This comprehensive study underscores the integration of theoretical and experimental approaches in advancing our understanding of complex chemical reactions.