Gamma-butyrolactones (GBLs) are signaling molecules produced by Streptomyces that play a key role in secondary metabolite production. Secondary metabolites, also known as natural products, have been used extensively in medicine and agriculture due to their bioactive properties. Genomic sequencing of the biosynthetic gene clusters (BGCs) from Streptomyces shows that only a small fraction of their secondary metabolites has been discovered. Activation of these silent BGCs has reinvigorated natural products chemistry as researchers become aware of the potential reservoir of novel lead compounds that remain unmined. One such GBL produced by Streptomyces is avenolide, responsible for activating production of avermectin, an anti-parasitic drug with over $850 million annual sales. In the work presented here, progress was made towards accessing the molecule avenolide in a synthesis commendable to derivatization with the aim of creating a library of avenolide-like molecules that could potentially “unlock” cryptic biosynthetic gene clusters and lead to the discovery of new bioactive secondary metabolites.

<p>The C-O single bond is found in numerous functional motifs including carboxylic acids,</p> <p>alcohols, and ethers. These compounds represent ideal precursors towards C-X (X = C, H, or heteroatom) bond formation due to their inherent stability and abundance in nature. As such, synthetic chemists continue to develop new technologies for the transformation of these precursors into biologically useful targets such as amides and amines. However, due to the stability of the C-O single bond, accessing such targets remains a consistent challenge. The activation of the carboxylic acids towards peptide synthesis has been facilitated through various coupling agents, including organoboron and transition metal catalysts. However, coupling agents can generate stochiometric, difficult-to-remove, toxic waste by-products.</p> <p>Organoboron/transition metal catalyzed condensations offer a more atom economical approach but suffer from varying degrees of optical erosion and poor sustainability. Phosphonium-based deoxyaminative technologies provide access to amines from alcohols via a phosphorus oxygen double bond formation driving force, but possesses a narrow nucleophilic nitrogen source scope, and poor atom economy. Transition metal/enzyme catalyzed “hydrogen borrowings” represent atom economical deoxyaminative alternatives. Still, their respective use of costly metals, and multiple enzymatic cascade steps severely limit the sustainability and scope of such protocols.</p> <p>An ambient deoxyamidation of carboxylic acids and deoxyamination of alcohols was</p> <p>developed through the use of N-haloimides activated by triphenylphosphine. Such</p> <p>technologies were found to possess broad functional tolerance and formed C-N bonds via a</p> <p>coupling to free amines, and the direct installment of the imide motif. Mechanistic experiments suggest that such transformations take place via the in situ generation of two separate phosphonium reactive species. </p>

<p>In recent years, sulfonyl fluorides have garnered significant attention in the synthetic organic and biochemical communities. Sulfonyl fluorides exhibit unique reactivity, as nucleophilic addition to the sulfur atom and subsequent elimination of fluoride only occurs under specific reaction conditions (otherwise known as SuFEx). Due to their inherent stability, sulfonyl fluorides are commonly used as biochemical probes to elucidate the structure of proteins. Sulfonyl fluorides also hold promise as irreversible covalent inhibitors. Despite the many potential applications of sulfonyl fluorides, methods to access this functional group remain underdeveloped, often requiring complex starting materials, or the use of hazardous reagents.</p> <p>Electrochemistry offers an attractive alternative to standard preparations of sulfonyl fluorides. Chapter 1 provides an overview of modern methods employed to synthesize sulfonyl fluorides, as well as key developments in synthetic organic electrochemistry. Chapter 1 closes with how the standardization of electrochemical reactions has allowed synthetic organic chemists to accurately reproduce electrochemical transformations.</p> <p>In Chapter 2, we developed an electrochemical method to access sulfonyl fluorides. The developed method operates by subjecting sulfones to electrochemical conditions, which initiates fragmentation of C–S bonds, and subsequent fluorination of a radical intermediate to realize the sulfonyl fluoride functional group. Early optimization focused on the synthesis of an optimal leaving group to bias the system towards formation of the desired sulfonyl fluoride in the presence of AgF₂. Once a leaving group was established, Lewis acids were screened in an attempt to activate the sulfone for substitution. Lewis acidic additives were later determined to serve as sacrificial oxidants as they did not chelate the sulfone starting materials. Reactions were run in divided and undivided electrochemical cells depending on the fluorinating reagent. Reactions with AgF₂ were run in an undivided electrochemical cell to prevent cathodic plating of Ag⁰. However, comparable results were achieved in an undivided electrochemical cell if AgF₂ was replaced with Selectfluor. Investigation into the incorporation of the leaving group into other substrates is ongoing. We hope to further develop this methodology to access complex sulfonyl fluorides and encourage the development of electrochemical methods in synthetic organic chemistry.</p>

<p dir="ltr">Both natural and synthetic macromolecules have gained significant attention over the last two decades as more and more applications have been developed for these types of compounds. In particular, drug delivery and sensing have seen great improvements with the use of biomimetic- and biomacromolecules. A key function for these macromolecules is selective recognition, which has evolved in nature over millions of years, but is difficult to replicate in the laboratory. An essential component of selective recognition is sequence definition of the host, which is a key characteristic found in biomolecules and is essential for the function of proteins and nucleic acids. In this work, I present new methods for creating biomimetic sequence-defined macromolecules through the synthesis of a new sequence-definable macrocycle, an amino acid-functionalized Fréchet-type sequence-defined dendrimer, and a range of new molecular cages. The molecular cages I present in this work are of varying sizes and with different endo- and exohedral functionalities intended for future use as selective recognizers.</p><p dir="ltr">The macrocycle presented in this work is the largest sequence-definable macrocycle reported to date with 20 functionalizable positions, synthesized via iterative exponential growth using a series of copper-catalyzed azide-alkyne cycloadditions (CuAACs). Synthesis of an amino acid functionalized fully sequence-defined Fréchet-type dendrimer was also attempted through a convergent synthesis via a series of CuAACs. However, in this project, I could only reach a second-generation dendron due to solubility issues. This issue should be resolvable in the future by adding solubilizing chains to the dendrons. Finally, a series of new large molecular tetrahedrons were synthesized, enabled by the development of a more facile synthesis of a previously developed vertex. This new methodology made it possible to quickly access large quantities of this key tetrahedron vertex. With the vertex, I was able to synthesize nine new molecular tetrahedrons of various sizes with pore openings of up to 33 Å and with volumes up to 17 nm³.</p>

<p dir="ltr">Borane-ammonia (BH₃-NH₃) has played an essential role in shaping and promoting the field of organic chemistry. However, we believe that the potential applications of BA in organic reductions have yet to be investigated. Our studies aimed to investigate BA as a reducing agent in organic reactions and to delve into the associated reduction mechanisms. In the second chapter of our research, we discovered that a combination of borane-ammonia and titanium tetrachloride (TiCl₄) has been explored as a versatile system for reducing various carbonyl compounds. By using BA with a small amount of TiCl₄ catalyst (10 mol%) in diethyl ether (Et₂O), we reduced different aryl and alkyl ketones into secondary alcohols at room temperature in just 30 minutes. This method is much faster than traditional uncatalyzed conditions, which usually take 24 hours or more to achieve the same reduction, and it does so without impacting other functional groups. Substituted cycloalkanones are selectively reduced to the thermodynamically favored product. Our deuterium labeling experiments found that the most probable pathway involves the hydroboration mechanism involving ketones and borane-ammonia in the presence of TiCl₄.</p><p><br></p><p dir="ltr">A slight variation in this chemical system can significantly impact the deoxyhalogenation process of aryl aldehydes, ketones, carboxylic acids, and esters. This process involves using a metal halide Lewis acid as a carbonyl activator, halogen carrier, and borane-ammonia. The selectivity of this process is determined by balancing the carbocation intermediate's stability with the Lewis acid's acidity. The choice of solvent and Lewis acid depends on the substituents present, and different substitution patterns have been explored. These principles have also been applied to selectively convert alcohols into alkyl halides. Furthermore, this system is used to selectively deoxygenate carbonyls of aldehydes and ketones into methyl and methylene hydrocarbons. The substituents on the benzene ring play a significant role in the deoxygenation process of carbonyl carbons in aldehydes and ketones.</p><p><br></p><p dir="ltr">In the third chapter of the study, various applications of the titanium system are examined. The TiCl₄/BH₃-NH₃ system was used to directly reduce a range of carboxylic acids to the corresponding alcohols at room temperature with good to excellent yields. This reduction method was achieved by adjusting the stoichiometry of borane-ammonia. This process is tolerant to various potentially reactive functional groups, such as N-protected amino acids, enabling the selective reduction of acids in the presence of amides and nitriles. Further, the titanium system was used to deoxygenation aromatic and aliphatic carboxylic esters into ethers. The ratio of borane-ammonia and catalyst controls the process. This method is the first practical borane-mediated process compatible with many sensitive functional groups and can convert challenging aromatic acid esters into ethers. Using BF₃–Et₂O as the catalyst changes the result products, reducing the esters to alcohols instead.</p><p><br></p><p dir="ltr">In the fourth chapter of our exploration, we looked at various applications of this system that involved reducing aliphatic and aromatic nitriles to primary amines. This was achieved by using 2.0 equivalents of <a href="" target="_blank">BH₃-NH₃ </a>and a molar equivalent of TiCl₄. We also found that the TiCl₄/BA system in dichloroethane (DCE) under reflux temperature efficiently reduces (deoxygenates) a range of aromatic and aliphatic primary, secondary, and tertiary carboxamides. We adjusted the catalyst and reductant stoichiometry accordingly, and the resulting amines were obtained in high yields using a simple acid-base workup.</p>

<p>In recent decades there has been great interest to produce novel bio-based composites to reduce carbon footprint without sacrificing the necessities that society demands. To achieve a more sustainable future, research in cellulose biopolymers has risen to the forefront. Impressive mechanical, thermal and optical properties along with its abundant biomass has made nanocellulose (NC) the subject of intense research in the area of electronics, drug delivery, sensors, selective filters, and structural materials, to name a few. The practical utility of any cellulose-based materials requires a more complete understanding of how the fundamental structure affects final performance. This thesis examines several avenues to obtain novel materials by considering processing parameters and preparation methods for working with raw nanocellulose materials, and mechanochemical approaches for surface grafting to obtain modified CNs with improved dispersion in organic media. Lastly, the synergy between the two studies and its impact on advanced materials and nanocomposites is discussed.</p> <p>The low cost and wide availability of cellulose nanofibers (CNF), a refined form of cellulose microfibrils, make these an ideal starting material for our studies. However, the aggregated states of freeze-dried CNFs hinder its use as an additive for reinforcing polymer blends or functional films. The use of <i>tert</i>-butyl alcohol (TBA) as a stabilizer in pharmaceutical drugs has been well studied for its effectiveness in facilitating redissolution and extending product shelf life. Lyophilization of aqueous CNF slurries treated with various amounts of TBA produced a more porous material that could be redispersed with superior colloidal stability relative to untreated freeze-dried CNFs. Furthermore, CNFs lyophilized from aqueous TBA mixtures could be subjected to mild mechanochemical reactions (horizontal ball milling) to produce esterified nanofibers with high degrees of substitution (DS) and good dispersibility profiles in organic solvents. This solventless technique allowed for a variety of carboxylic acids to be grafted onto CNF surfaces. Finally, investigations of new materials with technological utility have been explored using networks of CNFs modified with oleic acid. These can be cast into superhydrophobic (SHP) films having a hierarchical structure characteristic of a self-similar material, with a wettability comparable to that of the lotus leaf. The SHP surface can also be regenerated after surface fouling or physical damage. </p>

This thesis describes Further studies on the utilisation of the diterpenoid natural product , 12-hydrxypodocarpa-8,11,13-trim 19-oic acid* (podocarpic acid) (1) . In particular it describes transformations of the C-ring to give suitable intermediates for the synthesis of optically active steroids and terpenoids. An investigation has been carried out on the Birch reduction of 12-methoxypodocarpa-8,11,13-trien-19-ol (8), and conditions for the optimum formation of the ketonic products (10) and (12) are suggested. The enones (25) and (26) have been synthesised from 12-hydroxypodocarpa-8,11,13-trien-19-oic acid (1) by sequences involving reduction of the aromatic ring followed by ring C transformations. Methyl 12-hydroxypodocarpa-8,11,13-trien-19-oate (3) has been converted in ca. 60% yield to the dextrorotatory C 13 methyl ether which has then been reduced in good yield to the enone (163). Potential routes for conversion of the enones (25), (26), and (163)into steroidal analogues are described. Initial steps in the transformation of the C 13 methyl ether(62) into an intermediate (176) suitable for the synthesis of (+)-a-onocerin (80) have been investigated. A preliminary study on the synthesis of the C 14 phenol (190) or its methyl ether (191) is also reported. * The numbering system used throughout this thesis is that proposed by J.W. Rowe (personal communication to Professor R. C. Cambie) in "The Common and Systematic Nomenclature of Cyclic Diterpenes", 3rd Revision, Oct. 1966, to be submitted to the IUPAC Commission on Organic Nomenclature (see page 144)

This thesis describes Further studies on the utilisation of the diterpenoid natural product , 12-hydrxypodocarpa-8,11,13-trim 19-oic acid* (podocarpic acid) (1) . In particular it describes transformations of the C-ring to give suitable intermediates for the synthesis of optically active steroids and terpenoids. An investigation has been carried out on the Birch reduction of 12-methoxypodocarpa-8,11,13-trien-19-ol (8), and conditions for the optimum formation of the ketonic products (10) and (12) are suggested. The enones (25) and (26) have been synthesised from 12-hydroxypodocarpa-8,11,13-trien-19-oic acid (1) by sequences involving reduction of the aromatic ring followed by ring C transformations. Methyl 12-hydroxypodocarpa-8,11,13-trien-19-oate (3) has been converted in ca. 60% yield to the dextrorotatory C 13 methyl ether which has then been reduced in good yield to the enone (163). Potential routes for conversion of the enones (25), (26), and (163)into steroidal analogues are described. Initial steps in the transformation of the C 13 methyl ether(62) into an intermediate (176) suitable for the synthesis of (+)-a-onocerin (80) have been investigated. A preliminary study on the synthesis of the C 14 phenol (190) or its methyl ether (191) is also reported. * The numbering system used throughout this thesis is that proposed by J.W. Rowe (personal communication to Professor R. C. Cambie) in "The Common and Systematic Nomenclature of Cyclic Diterpenes", 3rd Revision, Oct. 1966, to be submitted to the IUPAC Commission on Organic Nomenclature (see page 144)

This thesis describes Further studies on the utilisation of the diterpenoid natural product , 12-hydrxypodocarpa-8,11,13-trim 19-oic acid* (podocarpic acid) (1) . In particular it describes transformations of the C-ring to give suitable intermediates for the synthesis of optically active steroids and terpenoids. An investigation has been carried out on the Birch reduction of 12-methoxypodocarpa-8,11,13-trien-19-ol (8), and conditions for the optimum formation of the ketonic products (10) and (12) are suggested. The enones (25) and (26) have been synthesised from 12-hydroxypodocarpa-8,11,13-trien-19-oic acid (1) by sequences involving reduction of the aromatic ring followed by ring C transformations. Methyl 12-hydroxypodocarpa-8,11,13-trien-19-oate (3) has been converted in ca. 60% yield to the dextrorotatory C 13 methyl ether which has then been reduced in good yield to the enone (163). Potential routes for conversion of the enones (25), (26), and (163)into steroidal analogues are described. Initial steps in the transformation of the C 13 methyl ether(62) into an intermediate (176) suitable for the synthesis of (+)-a-onocerin (80) have been investigated. A preliminary study on the synthesis of the C 14 phenol (190) or its methyl ether (191) is also reported. * The numbering system used throughout this thesis is that proposed by J.W. Rowe (personal communication to Professor R. C. Cambie) in "The Common and Systematic Nomenclature of Cyclic Diterpenes", 3rd Revision, Oct. 1966, to be submitted to the IUPAC Commission on Organic Nomenclature (see page 144)

This thesis describes Further studies on the utilisation of the diterpenoid natural product , 12-hydrxypodocarpa-8,11,13-trim 19-oic acid* (podocarpic acid) (1) . In particular it describes transformations of the C-ring to give suitable intermediates for the synthesis of optically active steroids and terpenoids. An investigation has been carried out on the Birch reduction of 12-methoxypodocarpa-8,11,13-trien-19-ol (8), and conditions for the optimum formation of the ketonic products (10) and (12) are suggested. The enones (25) and (26) have been synthesised from 12-hydroxypodocarpa-8,11,13-trien-19-oic acid (1) by sequences involving reduction of the aromatic ring followed by ring C transformations. Methyl 12-hydroxypodocarpa-8,11,13-trien-19-oate (3) has been converted in ca. 60% yield to the dextrorotatory C 13 methyl ether which has then been reduced in good yield to the enone (163). Potential routes for conversion of the enones (25), (26), and (163)into steroidal analogues are described. Initial steps in the transformation of the C 13 methyl ether(62) into an intermediate (176) suitable for the synthesis of (+)-a-onocerin (80) have been investigated. A preliminary study on the synthesis of the C 14 phenol (190) or its methyl ether (191) is also reported. * The numbering system used throughout this thesis is that proposed by J.W. Rowe (personal communication to Professor R. C. Cambie) in "The Common and Systematic Nomenclature of Cyclic Diterpenes", 3rd Revision, Oct. 1966, to be submitted to the IUPAC Commission on Organic Nomenclature (see page 144)