Organic Chemistry Commons^™

Structure-Activity Relationships Of Isothiourea And Silicon Phthalocyanine Catalysts, Christian J. Harrison

Theses and Dissertations

Efficient organic synthesis often relies on improving catalyst designs and investigating reaction mechanisms to accomplish feats such as high stereoselectivity, low catalyst loadings, and performing sustainable chemistry. Within the field of organocatalysis, intermolecular interactions between a catalyst and a substrate are a large contributing factor to the control of a reaction, including rate and selectivity. Investigating mechanisms can provide information on the type of intermolecular interactions occurring in the reaction, aiding future reaction and catalyst development. This dissertation will explore two recent projects and how probing intermolecular interactions through simple modifications provides information useful for new catalyst designs and properties. …

Modified N-Heterocyclic Carbene Catalysts For Polyurethane Synthesis, Charise D. Young

Pomona Senior Theses

Polyurethanes are widely used polymers synthesized from diisocyanate and diol molecules. They are ubiquitous polymeric materials with important industrial applications. Their increasing market value prompts the need for selective and efficient production which can be achieved through N-Heterocyclic carbene (NHC) catalysis. N-heterocyclic carbenes are heterocyclic molecules containing a carbene atom and at least one nitrogen adjacent to the carbene center. The nitrogen substituents on the adjacent nitrogen play an important role in influencing their steric and electronic properties and resultant reactivity.^1,2 There is a lack of a comprehensive understanding of the steric and electronic properties of NHCs and how …

Development Of Chiral Lewis Base Catalysts For Chlorosilane-Mediated Asymmetric C-C Bond Formations, Changgong Xu

Theses and Dissertations

The chiral hydrazine is a crucial structural motif that serves as pivotal structural elements in numerous natural products and biologically significant molecules. We are particularly interested in the catalytic asymmetric reduction of hydrazones, as well as the catalytic asymmetric propargylation and allenylation of hydrazones, because they provide direct pathways to these enantio-enriched chiral building blocks. In this work, we will explore the potential of two different categories of chiral Lewis base catalysts in the said transformations.

Developed by another student in our group, axial-chiral 3,3’-triazolyl biisoquinoline N,N’-dioxides derived catalysts are tested and demonstrated its capability in activating various hydrazone …

The Emergence Of Zerovalent Carbon Compounds From Structural Curiosities To Organocatalysts, Allegra L. Liberman-Martin

Biology, Chemistry, and Environmental Sciences Faculty Articles and Research

Low-valent main group compounds have reactivity patterns and properties reminiscent of transition metals. While divalent carbon compounds such as carbenes are widely studied ligands and organocatalysts, zerovalent carbon species have received considerably less attention. This perspective highlights the properties and reactivity of zerovalent carbon compounds, focusing on their first applications as organocatalysts for small molecule reduction and polymerization reactions.

Enantioselective Dearomatization Facilitated By Non-Covalent Interactions Of N-Heterocyclic Carbene Catalysts And Pyridinium Salts, Jack A. Patterson

Graduate Theses, Dissertations, and Problem Reports (ETD)

Dihydropyridines are a practical organic scaffold commonly used for their pharmaceutical properties. Nucleophilic dearomatization of pyridines has proven to be a useful method in obtaining dihydropyridines. By using N-heterocyclic carbene (NHC) organocatalysts, dihydropyridines can be synthesized with high regioselectivity of the 1,4 regioisomer over the 1,2- regioisomer but often with low enantioselectivity. By incorporating non-covalent interaction contact points, we hypothesize that enantioselectivity can be enhanced. By synthesizing numerous NHCs, each proposed to exhibit a different type of non-covalent interaction (i.e., hydrogen bonding or ion pairing), an understanding of the secondary interactions within this reaction system can be studied and …

Manipulation Of Noncovalent Interactions For The Synthesis And Use Of Natural Product Synthons, Alison P. Hart

Dissertations

Natural products are widely used in the pharmaceutical industry, in agriculture, and as specialty chemicals. Methodology development focuses on optimizing the key organic reactions to access these natural products while trying to limit the overall number of synthetic steps. Key bond forming strategies are sought to provide new ways to address carbon-carbon or carbon-heteroatom bonds. The advancement of new asymmetric reactions to generate enantiopure products from achiral starting materials is a vital area of research. The objectives addressed in this dissertation include: 1) the development of a general reductive conversion of esters to ethers with a broad substrate scope accessing …

Investigations Into Ring-Opening Polymerization Of Functionalized Ε-Caprolactones, Danielle N. Coderre, Matthew K. Kiesewetter

Senior Honors Projects

Polymers are defined as large molecules constructed from small, repeating units (monomers) which make up everyday items, such as: plastic bags and bottles, waterproof coatings, pipes, etc. H-bonding urea (U) or thiourea (TU) catalysts paired with base cocatalysts used for organocatalytic ring-opening polymerization (ROP) of cyclic esters have been shown to exhibit fast rates of polymerization and result in polymers with controlled molecular weights (Mn) and low polydispersity indexes (PDI). Additionally, organocatalytic ring-opening polymerization (ROP) techniques have been shown to be tolerant of the incorporation of functional groups into the monomer feed, which is vital for the catalytic synthesis of …

Organocatalyzed Synthesis Of Epoxides From Chalcones Utilizing Amino Acids, Sabrina N. Kegeler

Masters Theses

The epoxide functional group is important throughout the chemical and pharmaceutical industries, as well as in nature. In the chemical industry, epoxides are present in resins and fragrances. In the pharmaceutical industry, epoxide-containing compounds are used as intermediates in the manufacturing of drugs. In nature, many natural products contain epoxide groups and are used for medicinal purposes, and for models to create synthetic molecules.

One approach to epoxide synthesis involves the use of an alkene precursor, a base, and an oxidizing agent. This is where my investigations began. The first step was to optimize the epoxidation reaction, examining substrate scope, …

Asymmetric Transformations Catalyzed By Chiral Binol Alkaline Earth Metal Phosphate Complexes, Sri Krishna Nimmagadda

USF Tampa Graduate Theses and Dissertations

Small molecule hydrogen bond donors have emerged as versatile catalysts in asymmetric synthesis. Within this class, chiral BINOL phosphoric acid is regarded as one of the pioneer catalysts used in several asymmetric transformations. The ability of the catalyst to activate the substrates could be controlled in two different ways. (1) Dual activation/bifunctional activation of substrate by hydrogen bond interactions or ion pairing with phosphoric acid or (2) By forming chiral BINOL phosphate metal complex that could significantly alter the interactions in chiral space. In particular, chiral alkaline earth metal phosphate complexes have unique advantages as catalysts owing to the ubiquitous …

Accessing Medicinally-Relevant Scaffolds Via Organocatalyzed Cascade Reactions, Joshua Hadley Jones

Dissertations, Theses, and Capstone Projects

The field of asymmetric catalysis embodies the efforts of chemists to mimic the stereoselectivity routinely achieved by biological systems. Asymmetric organocatalysis, a sub-field of asymmetric catalysis, is broadly based on the catalytic activity of non-transition metal, small molecules that transmit chirality to substrates. This dissertation describes experimental work towards the construction of versatile, medicinally-relevant molecular scaffolds using chiral, diarylprolinol silyl ether organocatalysts. Specifically, these catalysts were used in 1-pot, iminium-enamine catalyzed cascade reactions to functionalize α,β-unsaturated aldehydes. A comprehensive review of iminium and enamine organocatalysis is provided, including its development towards iminium-enamine cascade reactions. This review provides background for the …

Chiral Phosphoric Acids And Alkaline Earth Metal Phosphates Chemistry, Tao Liang

USF Tampa Graduate Theses and Dissertations

Asymmetric synthesis and catalysis is one of the leading research areas in chemistry society, for its versatility and efficiency in obtaining chiral molecules that found the vast majority in natural active compounds and synthetic drugs. Developing asymmetric catalytic methodology is at the frontier in both industrial and academic research laboratories. Enantioselective organocatalysis has emerged as a powerful synthetic tool that is complementary to metal-catalyzed transformations. The development of chiral phosphoric acid and metal phosphate as catalysts has been a breakthrough in recent years. Chiral phosphoric acids have been shown to be powerful catalysts in many organic transformations. Moreover, chiral metal …

Chiral Phosphoric Acid-Catalyzed Acetalization And Iso-Pictet-Spengler Reactions, Matthew Jon Kaplan

USF Tampa Graduate Theses and Dissertations

The development of novel asymmetric reaction methodologies has been invaluable in both the academic and industrial world. In just 15 years, organocatalysis has provided a new means of developing asymmetric reaction methodologies using catalysts that are environmentally benign, relatively inexpensive, bench stable, and non-toxic. One development in organocatalysis that is important to our group in particular is chiral phosphoric acid-catalysis. BINOL-derived and VAPOL-derived phosphoric acids have proven to be excellent catalysts for a number of reactions.

The two projects I will discuss my efforts on are acetalization and iso-Pictet-Spengler reactions. These were projects that I performed during my first two …

Structure-Reactivity Studies Of Simple 4-Hydroxyprolinamide Organocatalysts In The Asymmetric Michael Addition Reaction Of Aldehydes To Nitroolefins, Fintan Kelleher, John Watts, Lien Luu, Vickie Mckee, Ed Carey

Articles

A series of simple 4-hydroxyprolinamides was synthesised and they were found to act as organocatalysts for the asymmetric conjugate addition of aldehydes to nitroolefins in excellent yields (98%), with complete diastereoselectivity (99:1, syn:anti) and enantioselectivity (98% e.e. for syn). Furthermore, the use of low catalyst loadings (5 mol%) and a low aldehyde molar excess (1.5 equivalents) were achieved.

Chiral Binol Metal Phosphate/Phosphoric Acid Catalyzed Enantioselective Addition Of Phosphorus And Sulfur Nucleophiles To Imines And Epoxides, Gajendrasingh Ingle

USF Tampa Graduate Theses and Dissertations

The research presented in this dissertation focuses on chiral BINOL metal phosphatephosphoric acid catalyzed enantioselective additions of phosphorus and sulfur nucleophiles to imines and epoxides. In chapter 2, we reported a new method to synthesize chiral amino phosphine oxides. The reaction combines N-substituted imines and diphenylphosphine oxide catalyzed by chiral magnesium 9-antryl phosphate. A wide variety of aliphatic and aromatic aldimines substituted by electron neutral benzhydryl or dibenzocycloheptene groups were excellent substrates for the addition reaction. The imines protected with dibenzocycloheptene protecting group provided better enantioselectivity than those protected with benzhydryl group, while both imines gave comparable yields. Also, …

Enantioselective Brønsted And Lewis Acid-Catalyzed Reaction Methodology: Aziridines As Building Blocks For Catalytic Asymmetric Induction, Shawn E. Larson

USF Tampa Graduate Theses and Dissertations

Chiral molecules as with biological activity are plentiful in nature and the chemical literature; however they represent a smaller portion of the pharmaceutical drug market. As asymmetric methodologies grow more powerful, the tools are becoming available to synthesize chiral molecules in an enantioselective and efficient manner.

Recent breakthroughs in our understanding of phosphoric acid now allow for Lewis acid catalysis via pairing with alkaline earth metals. Using alkaline earth metals with chiral phosphates is an emerging approach to asymmetric methodology, but already has an influential record.

The development of new conditions for the phosphoric acid-catalyzed highly enantioselective ring-opening of meso-aziridines …