No description available.

Presented herein is the development, optimization and mechanistic investigation of an Cu catalytic system for the oxidation of sp 3 C-H bond of simple arenes to form C-N bond in a direct manner. Due to the prevalence of nitrogen containing molecules among biologically active synthetic and natural compounds, synthetic chemists have always been motivated to develop new efficient ways to directly transform ubiquitous carbonhydrogen (C-H) bonds into carbon- nitrogen (C-N) bonds. Recent advances in transition metal catalyzed C-H amination has demonstrated that it is not only possible but also practical to functionalize C-H bonds that are often considered inert in one step, circumventing more classical, sequential functional group interconversion approaches. Existing catalytic systems that promote the transition metal-catalyzed, amination of sp 3 C-H bonds displayed certain limitations, especially the lack of built-in versatility and stability in their amination reagents. To overcome these drawbacks of these existing catalytic system, our group developed a new Cu amination protocol that deployed versatile hydroxylamine-based with general structure RSO 2 NH-OAc as amination reagents. Although the reactivity of the catalytic system ranges from moderate to good, the catalytic system provided promising results using simple arene substrates. Further detailed mechanistic studies revealed that the reaction undergoes an unprecedented two subsequent cycles divided by a major intermediate PhCH 2 (NTsOAc). The proposed mechanism is consistent with radical clock experiments, observed reaction profiles, the need for excess of substrate, and the documented role of the ligand in the catalytic system. The exciting proposed mechanism led to a new type of copper catalyzed amination reaction using N- fluorobenzenesulfonimide (NFSI) as oxidant, which overcomes the need to use an excess of substrate. A wide range of unactivated amines HNR 1 R 2 , including sulfonamide and benzamide, can be used as amine sources, which enables the installation of different nitrogen groups on benzylic sp 3 C-H bond of a variety of substrates in moderate to excellent yield. Moreover, mechanistic experiments and critical analysis of related reactivity in the literature provide insight into the catalytic cycle, resulting in a proposal that details the role of both oxidant and amine source in the new system.

Free radical cyclization methodology has been used extensively in synthesis for manipulation of complex molecules such as alkaloids, terpenes, carbohydrates, peptides and nucleic acids. The methodology has emerged as a result of work by physical organic chemists who determined rate constants for the most common radical reactions used in organic synthesis. A novel route to cyclic imines based on 5-exo radical cyclization was explored. The radical precursors were imines prepared from allylamine and readily available a-phenylselenenyl ketones. The synthesis of conformationally constrained bicyclic nucleosides is also reported using 5-exo and 6-exo cyclizations of hexenyl and heptenyl radicals in thymidine nucleosides. The nucleosides were incorporated in a 15mer antisense oligonucleotide via solid-phase oligonucleotide synthesis. The AONs with the modifications were tested for target affinity and stability and compared with the well known LNA modified AONs. The thesis discusses the unique qualities of these novel molecules and presents them as potential candidates for antisense therapeutic agents. Keeping up with the theme of intramolecular carbon-carbon bond formation, microwave induced carbodechalcogenation of chalcogenoanhydrides was explored. Poor generality in these reactions made us turn to transition metal catalysis for Sonogashira cross-coupling reactions using alkyl aryl and diaryl tellurides as coupling partners.

The development of a palladium-catalyzed intramolecular carboesterification of unactivated olefins is described. Olefin difunctionalization is a powerful tool for adding complexity to a molecule, and this formal [3+2] cycloaddition generates highly functionalized fused ring systems. Initially discovered by Dr. Yang Li in our group, it was found that when propiolic acids with a pendant terminal olefin were treated with 1 mol % Pd(MeCN)2Cl2, 3 equivalents of copper (II) chloride, and 3 equivalents of lithium chloride in acetonitrile at 50 °C, cyclization occurred in up to 90% yield. The optimization of this reaction and the extension to propiolamides and propargyl alcohols is described in this thesis. A mechanism involving a novel palladium-carboxylate species is proposed. Preliminary investigations into the synthesis of chiral sulfoxide pincer ligands are also described. The nucleophilic aromatic substitution of 1,3-dibromobenzene and 2,6-dichloropyridine with various thiols, followed by oxidation of the sulfides to sulfoxides is investigated as a route to the desired proligands.

The development of a palladium-catalyzed intramolecular carboesterification of unactivated olefins is described. Olefin difunctionalization is a powerful tool for adding complexity to a molecule, and this formal [3+2] cycloaddition generates highly functionalized fused ring systems. Initially discovered by Dr. Yang Li in our group, it was found that when propiolic acids with a pendant terminal olefin were treated with 1 mol % Pd(MeCN)2Cl2, 3 equivalents of copper (II) chloride, and 3 equivalents of lithium chloride in acetonitrile at 50 °C, cyclization occurred in up to 90% yield. The optimization of this reaction and the extension to propiolamides and propargyl alcohols is described in this thesis. A mechanism involving a novel palladium-carboxylate species is proposed. Preliminary investigations into the synthesis of chiral sulfoxide pincer ligands are also described. The nucleophilic aromatic substitution of 1,3-dibromobenzene and 2,6-dichloropyridine with various thiols, followed by oxidation of the sulfides to sulfoxides is investigated as a route to the desired proligands.

This thesis documents the development of novel synthetic methodologies for the incorporation of sulfur dioxide into organic molecules employing the amine-sulfur dioxide complex DABSO (vide infra). These developed processes serve to access a range of sulfonyl-containing (-SO₂-) compounds including sulfones and sulfonamides, via sulfinic acid precursors. <b>Chapter 1</b> provides an overview of the synthesis and applications of sulfonyl-containing compounds and the organic chemistry of sulfur dioxide. A comprehensive introduction to the developed uses of sulfur dioxide surrogates in organic chemistry is given. The synthetic utility of metal sulfinates towards accessing sulfonyl-containing compounds is also discussed. <b>Chapter 2</b> details the development of a one-pot sulfone synthesis via metal sulfinates generated from organometallic reagents and DABSO. Alkyl, alkenyl and (hetero)aryl sulfinates prepared from organolithium and Grignard reagents can be efficiently coupled with a range of electrophiles to access a range of products including diaryl, aryl-heteroaryl and &beta;-hydroxy sulfones. <b>Chapter 3</b> describes an array-compatible, one-pot sulfonamide synthesis employing metal sulfinates and N-chloroamines as in situ-generated intermediates. This employs DABSO and sodium hypochlorite (bleach) as simple reagents and organolithium, organozinc and Grignard reagents along with amines as readily-accessible building blocks. The robust nature of this methodology and its potential application in discovery chemistry is demonstrated with a 65-compound array synthesis. <b>Chapter 4</b> documents the development of a palladium-catalysed sulfination reaction of boronic acids to access a range of sulfonyl-containing compounds. This involved the establishment of a one-pot/one step synthesis of sulfones leading to the discovery of a redox-neutral, ligand-free sulfination procedure using DABSO and palladium(II) catalysis. Sulfinic acid derivatives can be generated and subsequently trapped in situ with a variety of electrophiles to furnish sulfones and sulfonamides. <b>Chapter 5</b> summarises the research and the potential future work. <b>Chapter 6</b> provides experimental details and data.

Environmental concerns have birthed an awareness of how we conduct ourselves as citizens of this planet. To reduce environmental impact, we have learned that we must be responsible stewards in all ranges of life: from buying locally grown food to how scientific research and industrial processes are executed. In the realm of chemical research, "green chemistry" has initiated the development of new, sustainable methods that make use of atom economy, step economy, and utilize renewable materials to minimize waste and production of toxic by-products. The formation of carbon-carbon bonds lies at the very heart of organic synthesis, and traditional methods for forming such bonds generally require the use of at least one stoichiometrically preformed organometallic reagent. This corresponds to at least one equivalent of metallic waste byproduct. The in situ formation of alkyl metal nucleophiles for carbonyl additions via hydrogenation of [pi]-unsaturates represents an alternative to use of preformed organometallic reagents. Comprising nearly 90% of the atoms in the universe, hydrogen is vastly abundant and very cheap. The Krische group seeks to contribute new technologies which make use of catalytic hydrogenation and transfer hydrogenation in the reductive coupling of basic chemical feedstocks. / text

Controlling the absolute stereochemistry of molecules is a major challenge to contemporary chemists. Achieving high enantioselectivity with catalytic amounts of a chirality transfer (or inducing) agent, and the ease of regenerating such catalysts is yet another challenge. Due to the involvement of various transition metal complexes, the relatively young field of enantioselective catalysis has emerged as a powerful tool for organic chemistry. In our efforts towards the synthesis of a universal catalyst, O'Donnell Schiff base derived tetradentate ligands were shown to catalyze dialkylzinc additions to aldehydes in high selectivity. The three pot synthesis of bifurcated dipeptides in very good yields and the mechanistic aspects of diethylzinc additions to aromatic aldehydes are described in this dissertation. The chiral Lewis acidic behavior of these ligands was supported by a mechanistic study done examining the nonlinear effect. Unlike bidentate ligands such as (-)-3-exo-N,N-dimethylaminoisoborneol (DAIB), the tetradentate ligands in this study show strictly linear behavior. Also, the linear free energy relationships studied by observing the enantioselectivity with respect to electron donating or withdrawing substituents on the benzaldehyde substrates supported a Lewis acid role for the zinc complexes. A negative slope was obtained when ee's were plotted against sigma values of the substituted benzaldehydes. Since they bind to various bivalent transition metal cations, these ligands can be viewed as privileged structures, and may potentially become catalysts for various asymmetric reactions. As catalyst screening can be greatly facilitated by heterogeneous catalysis, solid phase ligands were synthesized using Wang and Merrifield resin supports. The synthetic methodology was developed using a diarylketimine linker with the aid of on-bead characterization techniques such as 13C NMR and UV-VIS spectroscopy. The ligands were shown to asymmetrically catalyze the alkenylzinc additions to aromatic aldehydes. In situ generation of alkenylzinc reagents by boron to zinc transmetalation followed by the addition to benzaldehyde in the presence chiral zinc complexes resulted in enantiomerically enriched allylic alcohols. The preliminary results for this transformation resulted in 3:1 selectivity in favor of S-isomer.

No description available.

Despite the great abundance of C–H bonds in readily available starting materials, their use in synthesis of functionalized molecules has been hampered by the high bond strengths, rendering them inert to common organic reagents. However, recent progress in the field has addressed this issue, enabling selective C–H bond functionalizations to be performed using catalytic transition metal mediated processes. Herein, the use of sulfonyl chlorides as versatile reagents for C–H bond functionalizations is reported. Using chelation assistance, the regioselective conversion of C–H bonds to either C–S, C–Cl or C–C bonds was achieved. The methodology development, substrate scope determination and mechanistic investigations will be discussed.