Dissertations / Theses: 'Organic Chemistry Reactions - Selectivity'

1

Lu, Wenshuo 1971. "Organometallic reactions in aqueous media : reactivity, selectivity and synthetic applications." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=38077.

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Because of the concern for the environment and the search for the synthetic efficiency, the metal-mediated aqueous carbon-carbon bond formation reactions were studied. By employing sulfonimines, the scope of the metal-mediated aqueous Barbier-type allylation reactions was expanded to C=N electrophiles and the regio- and stereoselectivities of these reactions were examined.
The stereochemical factors in the indium-mediated aqueous Barbier-type allylation reactions of sulfonimines were investigated, and chelation control was observed and applied in the stereoselective crotylation reactions. By using chiral-modified sulfonimines or sulfinimines, the asymmetric aqueous Barbier-type allylation reaction of C=N electrophiles was also studied.
Highly regioselective propargylation reactions of sulfonimines mediated by zinc were discovered through the coupling of propargylic bromides with sulfonimines in aqueous media. Beyond the allylation transformations, zinc was also found as the metal of choice for the mediation of the Barbier-type benzylation reaction of sulfonimines and the coupling reaction of aldehydes with alpha-bromoacetonitriles in aqueous media.
The indium-mediated aqueous coupling reaction of 1,4-dibromobut-2-yne with aldehydes was demonstrated to be a concise way for the synthesis of 1,3-dien-ol compounds. Further synthetic applications of this reaction including the intro-molecular Diels-Alder reactions were preliminarily studied.

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2

Poingdestre, Sarah-Jane. "Exploring and exploiting selectivity in rhodium-catalysed hydroacylation reactions." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:f2993627-6550-42a5-b6e1-9d63f8268dbb.

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Chapter 1 is an overview of the key developments in rhodium-catalysed hydroacylation. The main focus of this chapter is the use of various chelation strategies for the stabilisation of key rhodium-acyl intermediates. In addition, the more recent emergence of regioselective hydroacylation processes has been highlighted. Chapter 2 discloses the branched-selective intermolecular hydroacylation of 1,3-dienes and S-chelating aldehydes to afford synthetically useful 1,5-dione products. The evaluation of a number of different phosphine ligands for this process identifies a correlation between ligand bite angle and reaction regioselectivity. Chapter 3 discusses the development of a linear-selective hydroacylation process for previously challenging alkyne substrates. This, in combination with a complementary branched-selective process, provides a ligand-controlled regioselectivity switch between the branched and linear pathways. Finally, Chapter 4 details efforts towards the development of multicomponent, tandem processes through exploitation of our synthetically useful branched hydroacylation adducts.

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3

Ganguly, Bishwajit. "Theoretical Studies Of pie-Facial Selectivity In Organic Reactions." Thesis, Indian Institute of Science, 1994. https://etd.iisc.ac.in/handle/2005/120.

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he thesis entitled "Theoretical Studies of pie-Facial Selectivity in Organic Reactions" involve a computational examination of a suitable reactivity problem in organic chemistry. Systematic and efficient -procedures have been developed and tested for rationalizing observed face selectivities in numerous substrates. In a number of cases precise transition state structures have also been computed in a rigorous manner. The molecules examined are by and large sterically unbiased. Considerable emphasis has been placed on obtaining general interpretations, In particular, the relative contributions of various sterio electronic and electrostatic effect have been considered in detail.Predictions of a-face selectivities haw also been made in a few cases. In recent years many mildly perturbed substrates have been shown to undergo pie-face selective reactions. Chapter 1 provides a brief review of the available experimental result involving nucleophilic, electrophilic, radical and Diels- Alder reactions.The current status of theoretical understanding of theae rasults is also summarized.The discussion includes qualitative proposal as well as quantitative calculations on selected substrates. The principal goals of the present work and general features of the MO methods used are briefly discussed.
Due to some technical problem in title page pie symbal is written as pie in word.

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4

Ganguly, Bishwajit. "Theoretical Studies Of pie-Facial Selectivity In Organic Reactions." Thesis, Indian Institute of Science, 1994. http://hdl.handle.net/2005/120.

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he thesis entitled "Theoretical Studies of pie-Facial Selectivity in Organic Reactions" involve a computational examination of a suitable reactivity problem in organic chemistry. Systematic and efficient -procedures have been developed and tested for rationalizing observed face selectivities in numerous substrates. In a number of cases precise transition state structures have also been computed in a rigorous manner. The molecules examined are by and large sterically unbiased. Considerable emphasis has been placed on obtaining general interpretations, In particular, the relative contributions of various sterio electronic and electrostatic effect have been considered in detail.Predictions of a-face selectivities haw also been made in a few cases. In recent years many mildly perturbed substrates have been shown to undergo pie-face selective reactions. Chapter 1 provides a brief review of the available experimental result involving nucleophilic, electrophilic, radical and Diels- Alder reactions.The current status of theoretical understanding of theae rasults is also summarized.The discussion includes qualitative proposal as well as quantitative calculations on selected substrates. The principal goals of the present work and general features of the MO methods used are briefly discussed.

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5

Diart, Valerie. "The control of selectivity in free radical reactions : a mechanistic and synthetic approach." Thesis, University College London (University of London), 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283194.

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6

Sovdat, Tina. "Toward understanding speed, efficiency and selectivity in retinal photochemistry." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:cfa19bb3-b399-4d26-9b9a-0ca1ff34dfa2.

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This Thesis describes the synthesis, structural, photochemical and photophysical studies of modified retinal protonated Schiff bases in solution. Ultrafast laser spectroscopy, NMR and circular dichroism studies were employed to investigate speed, yield and selectivity of photoisomerisation in these chromophores. Chapter 1 introduces relevant biological, photophysical and photochemical aspects of retinal protonated Schiff base photoisomerisation. It includes an overview of synthetic approaches to modified retinal synthesis pertinent to this this work. Chapter 2 discuses the investigation of the hypothesis that twisting of the chromophore’s isomerising double bond is responsible for ultrafast photoisomerisation in the protein environment. In these studies it was discovered that addition of a methyl group to the retinal backbone in solution results in protein-like photophysics. Chapter 3 presents photopysical and photochemical studies of modified all-trans retinal protonated Schiff bases that culminate in a qualitative model for the influence of electronic factors on photochemical and photophysical behaviour of these chromophores in solution. Chapter 4 describes structural and photophysical investigations of 11-cis retinal protonated Schiff bases. NMR studies indicate conformational flexibility of the chromophores. The first synthetic solution-based chromophore to reach rhodopsins’s speed of photoisomerisation is described. Chapter 5 presents an attempt to gain conformational information on retinal protonated Schiff bases using circular dichroism spectroscopy. Transfer of stereochemical information from the covalently attached stereogenic centre to the retinal backbone is demonstrated.

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Scatena, Gabriel dos Santos. "Multicomponent approach to silica-grafted peptide catalysts : A 3 D continuous-flow organocatalytic system with on-line monitoring of conversion and stereo-selectivity." Universidade Federal de São Carlos, 2014. https://repositorio.ufscar.br/handle/ufscar/8017.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
The derivatization of organocatalysts with functional appendages suitable to anchor onto solid supports is usually achieved by stepwise syntheses. As an alternative to such a strategy, this work describes a one-pot approach to silylated prolyl-peptide catalysts by a multicomponent reaction that enables the simultaneous incorporation of the catalytic and the heterogenizable (triethoxysilane) moieties. A microreactor with high catalytic efficacy and reproducibly in the conjugate addition of aldehydes to nitroolefins was obtained by grafting onto HPLC-grade silica (10 μm) and packing into a column with a selected catalyst. A 3 D continuous-flow system that includes the on-line monitoring of the reaction outcome was set up. For that, the microreactor was coupled to a chromatographic column for the separation of the remaining substrates from the Michael adduct in the second dimension, followed by a chiral polysaccharide column for the analysis of conversion and stereoselectivity. This approach represents a new instrumental setup that combines the advantages of multidimensional chromatography and flow catalysis.
A derivação de Organocatalisadores com apêndices funcionais adequados para ancorar em suportes sólidos é geralmente obtida por síntese “passo a passo”. Como uma alternativa para tal estratégia, este trabalho descreve uma abordagem de síntese one-pot de catalisadores prolil-peptio sililados através de uma reação multicomponentes, que permite a incorporação simultânea do sítio catalítico e o grupo funcional de ancoragem (trietoxisilano). Um micro-reactor foi obtido, tendo elevada eficácia catalítica e reprodutibilidade, na adição conjugada de aldeídos a nitro-olefinas, enxertando sobre sílica de grau HPLC (10 um) e preenchendo uma coluna com um catalisador escolhido. Um sistema de fluxo contínuo 3D que inclui a monitoração em linha do resultado da reação foi ajustado para cima. Para isso, o micro-reator foi acoplado a uma coluna cromatográfica para a separação dos substratos restantes do aduto de Michael na segunda dimensão, seguido por uma coluna de polissacarídeo quiral para a análise de conversão e estereosselectividade. Essa abordagem representa uma nova configuração do instrumento que combina as vantagens de cromatografia multidimensional e reações catálisadas em fluxo.

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8

Dimitroff, Martin. "Studies in [pi]-facial selectivity." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/nq20997.pdf.

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9

Michaud, Stephanie. "Exploring cathepsin B selectivity using epoxysuccinyl inhibitors." Thesis, McGill University, 2000. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=37782.

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There is accumulating evidence that cysteine proteinase activity plays an important role in cancer cell invasion and metastasis. Extracellular cysteine proteases, in particular cathepsin B, have been implicated in a variety of pathological processes involving tissue remodeling states, such as inflammation, parasite infection, and tumor metastasis, by degradation of extracellular matrix components. As such, increasing efforts are directed toward the development of inhibitors that are specific to the enzyme cathepsin B in order to both dissect out the role of the enzyme in these pathological processes and as potential therapeutic agents.
Unlike other members of the papain superfamily of enzymes, cathepsin B has a unique 18-residue insertion loop termed the "occluding loop" which sits over the primed subsites of the enzyme. It has now been well established that this loop is responsible for cathepsin B's unique dipeptidylcarboxypeptidase activity due to the presence of two positively charged residues, His110 and His111, that anchor the C-terminus of peptide substrates and allow the enzyme to carry out its carboxypeptidase activity. It has been demonstrated that this loop is a flexible segment that can move up and out of the way in order to accommodate binding of larger molecules such as the propeptide. Close examination of the x-ray crystal structure of the mature enzyme indicates the presence of an electrostatic interaction between the side chain of the main chain residue Asp22 and the imidazole ring of the occluding loop residue His110. This salt bridge acts as latch between the loop "open" and loop "closed" conformations of the enzyme.
It has been postulated that the development of inhibitors which interact with the "occluding loop" might provide highly selective inhibitors for cathepsin B and in fact cathepsin B-specific epoxysuccinyl inhibitors have been made which exploit the interaction of between a negatively charged carboxylate at P2' and the two positively charged histidine residues of the occluding loop. Using site-directed mutagenesis, we have dissected out the individual contributions of the two occluding loop histidine residues (His110 and His111). The effect of pH on these interactions has also been evaluated and it has been shown that increasing pH results in increased loop flexibility and diminished inhibitor potency.
Further structure-activity relationships for epoxysuccinyl inhibitors were also established by varying our inhibitor design template both in the P1' and P2' positions using known substrate specificities in these positions. Extension of the inhibitor template into the unprimed subsite region yielded the most potent epoxysuccinyl inhibitor to cathepsin B reported to date (BzlNH-Phe-NH-(2 S,3S)-tEps-Leu-Pro-OH: k2/Ki 2 900 000 +/- 300 000 M-1s-1).

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10

Ferguson, Douglas. "Selectivity of aryl and benzylic bromination." Thesis, University of Glasgow, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340755.

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11

Prangige, Erandi Sakunthala Peiris. "Product selectivity control in synthetic organic reactions by metal nanoparticle photocatalysis." Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/132075/1/Erandi_Prangige_Thesis.pdf.

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In this thesis, an in-depth study on alloying effect of non-plasmonic metals with gold nanoparticles to selectively control product formation under light and dark conditions was done. Overall, it was demonstrated that fine tuning the alloying effect could enhance product selectivity switch. This may open up a new research pathway for many important organic syntheses.

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12

Robinson-Surry, Julia M. (Julia Mae). "Pericyclic reactions in organic synthesis." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/65273.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2011.
Page 147 missing. Cataloged from PDF version of thesis.
Includes bibliographical references.
Part I of this thesis describes a formal, metal-free, [2 + 2 + 2] cycloaddition strategy based on a cascade of two pericyclic processes. An intramolecular propargylic ene reaction of a 1,6-diyne is used to generate a vinylallene, which then reacts in an inter- or intramolecular Diels-Alder reaction with an alkenyl or alkynyl dienophile. Reactions involving unsymmetrical alkenyl and alkynyl dienophiles proceed with good to excellent regioselectivity, and endo products are formed exclusively. The mechanism of several earlier fully intramolecular related transformations have been shown to involve an analogous process rather than the diradicalmediated pathways proposed previously. Part II of this thesis describes a [4 + 4] annulation strategy involving the intramolecular [4 + 2] cycloaddition of conjugated enynes with activated cyclobutene derivatives to access intermediates containing bicyclo[4.2.0]-2,4-octadiene moieties that then undergo electrocyclic ring opening reactions to provide 1,3,5-cyclooctatrienes. Five novel cyclooctatrienes have been prepared using this method. Part III of this thesis describes the use of supercritical carbon dioxide as an environmentally friendly alternative to conventional solvents for the synthesis of a variety of carboxylic amides. The addition of amines to ketenes generated in situ via the retro-ene reaction of alkynyl ethers provides amides in good yield, in many cases with ethylene as the only byproduct of the reaction. With the exception of primary, unbranched amines, potential side reactions involving addition of the amines to carbon dioxide are not competitive with the desired C-N bond-forming reaction. The amide synthesis is applicable to the preparation of p-hydroxy and P-amino amide derivatives, as well as amides bearing isolated carbon-carbon double bonds.
by Julia M. Robinson-Surry.
Ph.D.

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13

Larsson, Per-Erik. "Modelling Chemical Reactions : Theoretical Investigations of Organic Rearrangement Reactions." Doctoral thesis, Uppsala University, Department of Quantum Chemistry, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3475.

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Chemical reactions are ubiquitous and very important for life and many other processes taking place on earth. In both theoretical and experimental studies of reactivity a transition state is often used to rationalise the outcome of such studies. The present thesis deals with calculations of transition states in radical cation rearrangements, and a principle of least motion study of the rearrangements in the barbaralyl cation.

In particular, alternative quadricyclane radical cation (Q∙+) rearrangements are extensively studied. The rearrangement of Q∙+ to norbornadiene is extremely facile and is often used as a prototype for one-electron oxidations. However, electron spin resonance (ESR) experiments show that there are additional cations formed from Q∙+. Two plausible paths for the rearrangement of Q∙+ to the 1,3,5-cycloheptatriene radical cation are located. The most favourable one is a multistep rearrangement with two shallow intermediates, which has a rate-limiting step of 16.5 kcal/mol. In addition, a special structure, the bicyclo[2.2.1]hepta-2-ene-5-yl-7-ylium radical cation, is identified on these alternative paths; and its computed ESR parameters agree excellently with the experimental spectrum assigned to another intermediate on this path. Moreover, this cation show a homoconjugative stabilization, which is uncommon for radical cations.

The bicyclopropylidene (BCP) radical cation undergoes ring opening to the tetramethyleneethane radical cation upon γ-irradiation of the neutral BCP. This rearrangement proceeds through a stepwise mechanism for the first ring opening with a 7.3 kcal/mol activation energy, while the second ring opening has no activation energy. The dominating reaction coordinate during each ring opening is an olefinic carbon rehybridization.

The principle of least motion is based on the idea that, on passing from reactant to product, the reaction path with the least nuclear change is the most likely. By using hyperspherical coordinates to define a distance measure between conformations on a potential energy surface, a possibility to interpret reaction paths in terms of distance arises. In applying this measure to the complex rearrangements of the barbaralyl cation, a correct ordering of the conformations on this surface is found.

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14

Morley, Krista Louise. "Focusing mutagenesis into the active site to improve hydrolase selectivity." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=111830.

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Occasionally, researchers need to modify enzymes through amino acid substitutions to make them more efficient catalysts for organic synthesis. There is still debate over the best protein engineering strategy for improving enzyme enantioselectivity: rational design or directed evolution. Rational design experiments focus mutations close to the active site, while directed evolution experiments often find mutations far from the active site.
In this thesis, a combination of the two strategies improved Pseudomonas fluorescens esterase (PFE) for production of a useful synthetic building block for organic synthesis. Random mutagenesis within the active site increased enantioselectivity more effectively (up to 5-fold reaching E = 61) than random mutagenesis of the entire protein (only 1.5-fold reaching E = 19). A general survey of previously published enzyme improvements showed that closer mutations were more effective than distant mutations for improving enantioselectivity. On this basis, we proposed that random mutagenesis focused in the active site may dramatically increase the success rate in future directed evolution experiments. The X-ray crystal structures of three improved PFE mutants showed that mutations directly in the active site can increase enantioselectivity without significantly altering the shape of the binding pocket. For rationalizing the improved enantioselectivity, a crystal structure of a transition state analogue-complex provided the conformation of the fast reacting enantiomer and computer modeling determined the conformation of the slow reacting enantiomer.
When novel esterases are discovered from directed evolution experiments, they are screened with libraries of esters to identify their preferred substrates. A convenient method for the parallel synthesis of esters was developed by using solid-supported reagents to eliminate traditional purification.
Acetyl xylan esterase (AxeA) was examined as a potential catalyst for the production of chitosan, a biopolymer with many commercial applications. Screening for chitin deacetylase activity showed that AxeA preferentially deacetylates chitosan oligosaccharides over alkali-treated chitin and crystalline chitin.

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15

McLean, William Neil. "Metal catalysed reactions in organic chemistry." Thesis, University of Liverpool, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.257123.

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16

Ess, Daniel Halsell. "Quantum mechanical theory of reactivity and selectivity in organic and organometallic reactions." Diss., Restricted to subscribing institutions, 2007. http://proquest.umi.com/pqdweb?did=1456289591&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.

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17

Park, Seongsoon. "Enhancing hydrolase activity and selectivity by medium, substrate, and protein engineering." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=83088.

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Researchers use enzymes for enantio- and regioselective reactions because of their high selectivity and activity toward natural substrates. However, researchers sometimes need to modify the reaction system or the enzyme itself to get reliable selectivity and activity when they deal with unnatural substrates. To obtain researcher's need, one can change the solvent, modify the substrates, or alter the enzyme itself. These processes are called medium, substrate, and protein engineering, respectively.
This thesis deals with hydrolases, which are classified by EC 3. We applied the proper approach to improve their activity and selectivity depending on the reactions. For the first approach, highly polar ionic liquids were applied to lipase-catalyzed acylation. Ionic liquids worked reliably in enantio- and regioselective lipase-catalyzed reactions. In particular, ionic liquids dissolved polar substrates such as glucose and L-ascorbic acid, thereby facilitating their acylations. In the second approach to improving enantioselectivity of CAL-B (Candida antarctica lipase B) in beta-lactam ring opening reactions, we changed the nucleophile from water to a range of alcohols. Longer, secondary alcohols increased the reaction rate as well as the enantioselectivity. Molecular modeling revealed that the high enantioselectivity of CAL-B and the critical role of alcohols. For the last approach, structure-guided random mutagenesis was applied to increase the enantioselectivity of PFE ( Pseudomonas fluorescens esterase) toward MBMP (methyl 3-bromo-2-methylpropionate). The homology model was used to select amino acid residues for mutagenesis near the stereocenter of the docked tetrahedral intermediate of the substrate. Randomization of these residues yielded a Val122Ser mutant with E increased to 61 (from 12 of wild type enzyme), as well as a Val122Met mutant to 36.

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18

Boursalian, Gregory Bagrad. "Reactivity and Selectivity in Aryl C–H Functionalization by Electrophilic Radicals." Thesis, Harvard University, 2016. http://nrs.harvard.edu/urn-3:HUL.InstRepos:33493437.

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Two main challenges hinder the development of new, broadly useful C–H functionalization reactions: (1) most C–H bonds constitute part of the relatively inert backbone of an organic molecule, so it is difficult to elicit sufficient reactivity from these bonds, and (2) C–H bonds are ubiquitous in organic molecules, so it is difficult to control the selectivity of which C–H bond is functionalized. The subject of this thesis is the functionalization of C–H bonds in aromatic molecules. In addition to the relevant background, herein are described two new reactions which address the challenges of reactivity and selectivity in C–H functionalization described above. In Chapter 1 is described a new reaction in which an amine-N-oxide-ligated palladium complex, in conjunction with a silver cocatalyst, catalyzes imidation of arenes by the reagent N-fluorobenzenesulfonimide. The reaction enables imidation of a variety of arenes at or below room temperature, requires no coordinating directing group on the substrate, and gives synthetically useful yields with the arene as the limiting reagent. Mechanistic data is presented which implicates an unusual mechanism devoid of commonly invoked organometallic intermediates: oxidation of the palladium catalyst occurs as the turnover-limiting step, while C–H bond functionalization occurs subsequently at a higher oxidation state of the catalyst. The unusual imidation reactivity is ascribed to unique features of the amine-N-oxide ligand, which are also discussed. Described in Chapter 2 is a new radical aromatic substitution reaction with nearly complete para selectivity for a variety of monosubstituted arenes. We present a rationale for the unprecedented degree of positional selectivity exhibited by the reaction: we propose that arene-to-radical charge transfer in the transition state of radical addition, elicited by the unusually high electron affinity of the radical, is the factor primarily responsible for the positional selectivity. The utility of the reaction is illustrated by a direct synthesis of aryl piperazines, a common motif in medicinal chemistry.
Chemistry and Chemical Biology

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19

Ke, Tao 1972. "Mechanistic studies of enzymatic stereo-selectivity in aqueous and organic media." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/85241.

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20

Cadman, M. L. F. "Magnesium chelation and organic reactions." Thesis, University of Nottingham, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384304.

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21

Rahman, Ajara A. "Effects of Nucleophile Strength on Selectivity in BiBr3 Catalyzed Cyclic Ether Construction." W&M ScholarWorks, 2012. https://scholarworks.wm.edu/etd/1539626934.

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22

Hamberg, Anders. "Serine Hydrolase Selectivity : Kinetics and applications in organic and analytical chemistry." Doctoral thesis, KTH, Biokemi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-12831.

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The substrate selectivities for different serine hydrolases were utilized in various applications, presented in papers I-VI. The articles are discussed in the thesis in view of the kinetics of the enzyme catalysis involved. In paper I the enantioselectivities towards a range of secondary alcohols were reversed for Candida antarctica lipase B by site directed mutagenesis. The thermodynamic components of the enantioselectivity were determined for the mutated variant of the lipase. In papers II-III Candida antarctica lipase B was engineered for selective monoacylation using two different approaches. A variant of the lipase created for substrate assisted catalysis (paper II) and three different variants with mutations which decreased the volume of the active site (paper III) were evaluated. Enzyme kinetics for the different variants were measured and translated into activation energies for comparison of the approaches. In papers IV and V three different enzymes were used for rapid analysis of enantiomeric excess and conversion of O-acylated cyanohydrins synthesized by a defined protocol. Horse liver alcohol dehydrogenase, Candida antarctica lipase B and pig liver esterase were sequentially added to a solution containing the O-acylated cyanohydrin. Each enzyme caused a drop in absorbance from oxidation of NADH to NAD+. The product yield and enantiomeric excess was calculated from the relative differences in absorbance. In paper VI a method for C-terminal peptide sequencing was developed based on conventional Carboxypeptidase Y digestion combined with matrix assisted laser desorption/ionization mass spectrometry. An alternative nucleophile was used to obtain a stable peptide ladder and improve sequence coverage.
QC20100629

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23

Shunatona, Hunter Paul. "Catalyzed Intramolecular Aminocyclization Reactions." Thesis, University of California, Berkeley, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3640640.

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The scope of my doctoral studies was intended to address the specific synthetic challenge of the construction of heterocycles. As a result, the synthesis of nitrogen-containing heterocycles has been a key research focus during my graduate career and with this in mind, new methods for their construction were investigated.

In Chapter 1 of this dissertation, an aminoarylation reaction methodology was developed. This system utilized gold catalysis to accomplish an intramolecular aminocyclization followed by a aryl cross-coupling event to accomplish an overall aminoarylation. The strong oxidant Selectfluor was chosen as the terminal oxidant in the reaction due to its previous use in metal-catalyzed reactions. Experimentation and literature precedent led to the use of a bimetallic gold complex to facilitate the Au(I)–Au(III) oxidation which is typically a synthetic challenge. An unusual reaction mechanism was proposed for this reaction as a result of experimental probing in conjunction with a series of DFT calculations. This oxidative gold-catalyzed aminoarylation was found to provide access to a variety of heterocycles in a racemic fashion.

The second chapter continues with the theme of aminocyclization reactions but focuses on developing an asymmetric methodology. Previous work in our group had shown that dicationic Selectfluor is insoluble and generally unreactive in non-polar organic solvents. This reagent could be rendered useful after undergoing a phase-transfer event when used with lipophilic chiral phosphoric acids and accomplishing an enantioselective fluorination. However only cyclizations involving oxygen nucleophiles were disclosed. With this in mind, studies were undertaken to extend this phase-transfer technology towards aminocyclization reactions. It was found that an enantioselective 1,4-fluoroamination reaction could be accomplished with different diene substrate scaffolds.

Chapter 3 concentrates on another extension of the phase-transfer methodology utilizing a aryldiazonium salts. Literature precedent had shown that the terminal nitrogen of these reagents could serve as electrophiles for carbon-based nucleophiles, and their monocationic nature would allow for them to be sparingly soluble in organic solvents, thus revealing them as ideal candidates for phase-transfer reactivity. The reaction of these electrophilic nitrogen sources with tryptamine-based substrates allowed for the enantioselective construction of C3-functionalized pyrroloindolines which are an exotic framework found in natural products. The diazenated pyrroloindoline products could be further elaborated using photochemistry to provide C3-arylated compounds, exhibiting the versatility of this methodology for the construction of C–C or C–N bonds at the C3 position on the pyrroloindoline scaffold.

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24

Hitchcock, Stephen A. "Radical macrocyclisation reactions in organic synthesis." Thesis, University of Nottingham, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334845.

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25

Iqbal, Zafar. "Catalysis of organic reactions on clay." Thesis, Cardiff University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254656.

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26

Boyd, Susan Mary. "Asymmetric cycloaddition reactions." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293374.

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27

Green, Stuart P. "Biomimetic radical reactions." Thesis, University of Nottingham, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357914.

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28

Mahal, Amrik Singh. "Asymmetric aldol reactions." Thesis, University of Kent, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302987.

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29

Aiyub, Zaharah. "Reactions of silyldiynes." Thesis, University of Sussex, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385058.

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30

Bisnaire, Michel M. J. "Iron-mediated allylic alkylation reactions." Thesis, University of Ottawa (Canada), 1990. http://hdl.handle.net/10393/5797.

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In this work it will be shown that Fe(CO)$\sb2$(NO)$\sb2$ mediated allylic alkylation reactions proceed via an intermediate which is neither an $\eta\sp3$-allyliron complex nor an $\eta\sp2$-allyliron complex. Rather, (Fe(CO)(NO)$\sb2$DMM)$\sp-$Na$\sp+$ has been identified as the catalytic intermediate. This provides the first evidence of an interaction between the nucleophile and the metallic center in reactions involving iron nitrosyl complexes. The study of the Fe(CO)$\sb3$(NO)$\sp-$Na$\sp+$, geranyl acetate, and NaDMM system was studied in order to elucidate the catalytically active species. Although it was determined that Fe(CO)$\sb3$(NO)$\sp-$Na$\sp+$ served as the precursor of a catalytic species X, the nature of X remains unknown.

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31

Maughan, K. "Grignard reactions with lactones." Thesis, University of Nottingham, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356029.

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32

Wilmshurst, Martin Philip. "Fluoroalkyl radical cyclisation reactions." Thesis, University College London (University of London), 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286192.

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33

Chauncey, Marek Anthony. "Reactions heterocyclic quinone methides." Thesis, University of Ulster, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328193.

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34

Bird, Andrew James. "Zirconium-mediated cyclisation reactions." Thesis, University of York, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319766.

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35

Stones, P. A. "New ring forming reactions." Thesis, University of Southampton, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373984.

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36

Jackson, Kelvin E. "Development and application of computational tools to analyse selectivity in organic chemistry." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:16ccc310-0cf4-44f6-b999-adb451f0f873.

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The work described in this thesis illustrates how a range of computational methods may be applied to explain, both experimentally observed and computationally predicted, selectivity, in the field of Organic Chemistry. We begin with a discussion of the theory behind Computational Chemistry and also background to the ever growing field of organocatalysis, followed by a synopsis on the importance of asymmetry in synthesis. The second chapter focusses on an asymmetric organocatalysed reaction for the diastereoselective and enantioselective synthesis of the morphan motif. We look at a range of primary amine organocatalysts in this section, and are able to account for the observed asymmetry that is imparted, both qualitatively and quantitatively. Furthermore, through the course of our investigation, we were able to propose synthetic modifications to an existing organocatalyst used in this reaction, resulting in improvement to the enantioselectivity and atom economy of the reaction. In chapter three, we examine the various factors influencing ring closing reactions for a range of systems and investigate the origin of the underlying preference for cyclisations to follow Baldwin's rules for selectivity. In order to do this, we use a range of computational techniques, including nucleus independent chemical shift (NICS) analysis to gain a better understanding of the magnetic properties of ring closing transitions structures (TS). Chapter four contains an in depth look into the stereoelectronic effects altering enantioselectivity in alkylation reactions with bicyclic enamine chiral auxiliaries. In this study, we were able to develop, improve, and implement a new methodology for explaining stereoselective alkylations of tropane-type enamine systems. Our computationally derived predictions of selectivity made for a number of systems have been subsequently verified with experimental results which were within 5 kJ/mol of our values. In chapter five, we use computational analysis to provide insight into the regiodi-vergent a- and a'-lithiation-electrophile trapping of N-thiopivaloyl- and N-(tert- butoxythiocarbonyl)-a-alkylazetidines. We calculated the magnitudes of rotational barriers for a range of protected azetidine systems and showed that rotamer interconversion could not occur for the aforementioned species at the temperature and on the time scale of the lithiations. In the final chapter, we describe the development of computational tools that have been essential in the other investigations discussed in this thesis. We also look at potential future applications of these programs in the field of Organic Chemistry.

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37

Krupa, Joanne C. (Joanne Christine). "Coenzyme analogs in dehydrogenase-catalyzed reactions." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39934.

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To enhance the performance of dehydrogenases in synthetic organic chemistry, coenzyme analogs of NAD(P)$ sp+$/NAD(P)H were examined. Our study shows that dehydrogenases are more efficient with NAD(P)$ sp+$ than with the APAD(P)$ sp+,$ FPAD$ sp+$ or SPAD(P)$ sp+$ under non-regenerating oxidative conditions in terms of yields. Under regenerating conditions, APAD$ sp+$ often exceeded NAD$ sp+$ in terms of product formation. Lower yields were observed with SPAD(P)$ sp+$ and FPAD$ sp+.$ These coenzyme analogs also displayed reduced reactivity, but APAD$ sp+$ was the most promising of the three. In reduction experiments, the analogs are as equally or slightly less efficient as NAD(P)H in terms of yields, but react slower. Electropotentials could not explain all of the variation in yields. Therefore, to better understand the interactions made by the 3-substituent of the nicotinamide ring in the dehydrogenase active site, the binding properties of 1-methyl-3-substituted pyridinium salts (iodide and chloride) to 8 different dehydrogenases were examined. The salts were R = CONH$ sb2,$ COONa, CN, CH$ sb3,$ CONHCH$ sb3,$ CH$ sb2$OH, CH$ sb2$CN, Cl, H, CH(OH)$ sb2,$ COOCH$ sb3$ and COCH$ sb3$ did not bind well into the active site. However, the five compounds that did bind, in order of their observed increased inhibitory effects are R = CH=NOH, CONHNH$ sb2,$ CSNH$ sb2,$ NH$ sb2$ and ONa. The ONa chloride salt binds on average 336 times more tightly than CONH$ sb2.$ It is proposed that the tightly bound compounds with electron-withdrawing substituents (CH=NOH, CONHNH$ sb2,$ CSNH$ sb2)$ and pKa's in the range of 9.4-10.4 form stronger hydrogen bonds and the two with strong electron-donating groups (ONa and NH$ sb2)$ with low pKa's in their protonated forms bound in a geometry optimized for efficient hydrogen bond exchange.
The difference in binding between the nicotinamide and thio derivatives can be geometry related. The X-ray crystal structure of 1-methyl-thionicotinamide shows a different ground state orientation (s-cis) than that previously reported for 1-methyl-nicotinamide (s-trans). From ab initio calculations, the thio derivative has a global and local minima at $ approx$30$ sp circ$ and 135$ sp circ$ as compared to 0$ sp circ$ and 180$ sp circ$ respectively for the oxygen compound. However, both compounds have an out-of-plane conformation in crystal. The enzyme favored trans out-of-plane conformation may also be more easily accessible for the thio than the oxygen derivative since the equilibrium constant for the cis to trans process is favored by a factor of 5.4.
By extension, the geometry that SPAD(P)$ sp+$ adopts to maximize hydrogen bond formation may cause it to have a slow turnover rate and to be an inefficient hydride acceptor, while APAD(P)$ sp+$ which is not as tightly bound to dehydrogenases, is a more efficient coenzyme.

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38

Wang, Haofan. "Synthesis and reactions of organoiron compounds." Diss., The University of Arizona, 2003. http://hdl.handle.net/10150/289994.

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The multistep synthesis of the redox active adenine analog [e]-ferrocenyl-4-aminopyrimidine is reported. The redox active system will be incorporated into oligonucleotides to study the electron transfer through the molecular pi-system of DNA in future studies. Attempts were made to synthesize a cyclopenta-4-aminopyrimidine derivative which possesses an endocyclic double bond in the cyclopentane ring. This intermediate can be subsequently coupled with cyclopentadienyl iron dicarbonyl (Fp) group and, after thermal decarbonylation, form the desired ferrocene ring. Many double bond precursors are prepared, including dibromide, acetate, alcohol, ketone and phenylseleno derivatives of cyclopentapyrimidine. However efforts to form an endocyclic double bond turned out to be unsuccessful. Exocyclic double bond derivatives of cyclopentapyrimidine have also been prepared. An improved chiral synthesis of [e]-ferrocenyl-4-aminopyrimidine is achieved, in which a Curtius rearrangement to form an O-benzylcarbamate was done using a formyl ferrocene carboxylic acid. The yield of the final cyclization step was also greatly improved. The synthesis of methyl-(2,5-dimethoxy-4-fluorophenyl)-acetate, a thymine isostere precursor, is reported. It will be used as a substitute for a thymine base in a peptide nucleic acid (PNA) synthesis in the future. Regioselective bromination of 2-fluoro-hydroquinone introduced a bromo group at the desired position. After protection of hydroxyl groups in this product, a carboxylic acid ethyl ester group was introduced. Finally, an Arndt-Eistert reaction was used to extend the carboxylic acid by one carbon to the corresponding phenyl acetic acid ethyl ester. A chemical model mimicking the biosynthesis of the cyanide ligand in the enzyme hydrogenase is developed. In this model a thiocarbamate is first formed and subsequently dehydrated by polyphosphate ethyl ester(PPE) to make a thiocyanate. Finally, the cyanide moiety is transferred to the metal center. The direct dehydration of a carboxamidoiron species to form a cyano ligand is also reported.

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39

Nilsson, Peter. "Selectivity in Palladium- and Enzyme-Catalyzed Reactions : Focusing on Enhancement of Reactivity." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3625.

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40

Daniels, David S. B. "Reactions of allenylpalladium intermediates in organic synthesis." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:61054889-d0ac-4d08-96a7-2e05fb3aa455.

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This thesis describes our examination of the reactivity of allenylpalladium intermediates generated from the reaction of palladium(0) with propargylic electrophiles. Chapter 1 provides a general overview of the literature reported to date concerning the nature and reactivity of allenylpalladium intermediates. The coupling of a variety of propargylic electrophiles with aryl boronic acids to form allenes is examined in Chapter 2. However, when employing diastereomerically pure electrophiles, some erosion of stereochemistry was observed in the allene products. This effect was examined further, and epimerisation of the allene product was found to be the origin of the loss of stereochemistry. Evidence for the species likely responsible for this epimerisation is presented. The serendipitous formation of tetrahydrofurans (THFs) from propargylic 7-membered cyclic carbonates prompted an in-depth examination of this reactivity, as described in Chapter 3. The reaction of these cyclic carbonates was rendered stereoselective and the stereochemical outcome of the reaction elucidated. The methodology was extended to propargylic acyclic carbonates which allowed the formation of tetrahydropyrans (THPs). The effect of ring-size and substituents on the cyclisations was examined, culminating in the formation of two rings in a single step from diol-containing bis-carbonates. Chapter 4 describes the extension of this methodology to the formation of azacyclic products. This built upon foundation work conducted by a Part II student within the group, and further improved the selectivity of the reaction. Two diverse azacyclic skeletons could be formed from the same substrate by the employment of different bidentate phosphine ligands, and a variety of substrates were examined under these conditions. Chapter 5 draws general conclusions and sets out possible future directions for the methodology, and full experimental details are outlined in Chapter 6.

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41

Knipe, Peter Clarke. "Chiral counter-ion controlled asymmetric electrocyclic reactions." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:c981f724-c783-4913-b224-92fcebf94d37.

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The aim of this project was to develop new catalytic methods to control asymmetry in electrocyclic reactions, and to apply these methods to generate complex molecules. Initial efforts were directed towards the catalysis of anionic 8π electrocyclizations (Chapter 2 and Figure i). 8π electrocyclization was not achieved due to issues with alkene geometry and anion stability. Our efforts were then directed towards using phase-transfer catalysis to generate complex polycyclic compounds via a cascade electrocyclization-1,4-addition (Chapter 3 and Figure ii). Pyrrolidines and indolizidines were generated in excellent yield from simple starting-materials with high levels of stereocontrol. Finally, we investigated the catalysis of a 6π [1,6] electrocyclization to generate dihydroquinolones (Chapter 4 and Figure iii). A novel BINOL-derived copper(II) catalyst was developed, and afforded dihydroquinolones directly from their amine and aldehyde precursors with good yields and enantioselectivities.

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42

Bathgate, Antoinette. "Syntheses & reactions of azabicycles." Thesis, University of Leicester, 1988. http://hdl.handle.net/2381/33896.

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Several novel nitrogen containing bicyclic systems have been synthesised and their chemistry investigated. The kinetic and thermodynamic invertomer ratios of N-chloro-1,2,3,4-tetrahydro-2-keto-l, 4-iminonaphthalene derivatives were determined. The results suggested that a repulsive interaction existed between the positive end of the carbonyl dipole and the incoming electrophilic chlorine. Despite reaction under favourable solvolytic conditions, it appeared that homolysis of the N-chloroamines was favoured over heterolysis. Under conditions of negligible inversion, N-chloro-1,4-dihydro-1-methyl-l,4-iminonaphthalenes underwent heterolytic rearrangement to form 4-inethyIquinclines. From these experiments it was deduced that the quinoline products must be derived from the anti-N-chloroamines with loss of a bridgehead carbon atom. A mechanism for the formation of these products was proposed. Nortropane was synthesised in high overall yield and the first synthesis of a simple derivative of nortrop-6-ene which has been achieved in significant yield was also accomplished. The procedure demonstrated the viability of an intramolecular cyclisation approach given an appropriately nucleophilic nitrogen. Investigation of the reactions of chlorosulphonyl isocyanate with 7-substituted cycloheptatrienes provided evidence that choice of solvent and reaction time along with careful monitoring exerts control over the addition of either the C=0 or C=N moiety across the termini of the triene unit.

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43

Mugford, Paul F. "Expanding hydrolase catalyzed reactions to new substrates and reactions : subtilisin catalyzed hydrolysis of sulfinamides and sterically hindered substrates." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=102684.

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Enzymes are increasingly applied to organic synthesis because of their high enantioselectivity, chemoselectivity, and environmental friendliness. Hydrolytic enzymes are the largest class used for biotransformations, and subtilisin is one of the commonly used serine proteases for organic synthesis. We hypothesized that we could expand the usefulness of subtilisin to hydrolyze unnatural substrates. The X-ray crystal structure of subtilisin shows that it has a large open active site. Previous workers focused on hydrolysis of natural substrates and close analogs, but the open active site suggests that subtilisin should accept bulky substrates that do not resemble peptides.
The Diels-Alder reaction is important in organic synthesis because it has the potential to create several stereocenters in a single step. We resolved a bulky secondary alcohol ester of a spiro chiral auxiliary for the Diels-Alder reaction on a gram scale using subtilisin Carlsberg. The reaction proceeded with high enantioselectivity and yield. Cholesterol esterase showed high enantioselectivity but with the opposite enantiopreference, consistent with mirror image arrangement for the active sites of subtilisins and lipases/esterases. We also used molecular modeling to identify the molecular basis of enantioselectivity of subtilisin Carlsberg toward this secondary alcohol.
Resolution of tertiary alcohol esters is difficult because they are also very bulky, but important because there are only a few synthetic and biocatalytic methods to prepare enantiopure tertiary alcohols. We discovered several proteases that hydrolyze esters of tertiary alcohols, one of which was subtilisin Carlsberg. This is the first examination of protease hydrolysis of tertiary alcohol esters. Substrate studies and molecular modeling explained their reactivity and enantioselectivity.
Sulfinamidies are also bulky substrates, but surprisingly subtilisin catalyzed a catalytic promiscuous reaction of N-acyl sulfinamides. Subtilisin Carlsberg-catalyzed hydrolysis of N-acyl sulfinamides favored cleavage of the sulfinamide (S(O)-N) bond with a minor amount of the expected carboxamide (C(O)-N) bond. The sulfinamide hydrolysis was enantioselective and confirmed by product isolation from the S-N sulfinamide cleavage. In contrast, the related subtilisins BPN' and E favored the C-N carboxamide hydrolysis.
Further examination using electrospray-mass spectrometry revealed a sulfinyl-enzyme intermediate located at the active site, analogous to an acyl-enzyme. This suggested an analogous mechanism to the amide/ester hydrolysis. Substrate variation indicated a substrate reversal was responsible for the change in reactivity by binding in the S1 acyl pocket. Three mutations of subtilisin BPN' towards subtilisin Carlsberg increased the S-N hydrolysis by 14-fold, indicating that only a few mutations were responsible for the catalytic promiscuity. The substrate specificity and mutagenesis were consistent with a reversed orientation for the sulfinyl hydrolysis reactions.
The active site of subtilisin is indeed versatile for unnatural substrates and unnatural reactions. We expanded the applications of subtilisin to resolve bulky substrates, such as chiral auxiliaries and tertiary alcohol esters, and also to perform a new catalytic promiscuous sulfinamide S-N bond hydrolysis. Based on these results, subtilisin should prove useful for future resolutions of bulky substrates, and also in catalytic promiscuous reactions where unusual reactive centers are hydrolyzed.

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44

Banks, Jeffrey T. "Multiple photon reactions of organic molecules in solution." Thesis, University of Ottawa (Canada), 1994. http://hdl.handle.net/10393/6788.

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This thesis presents the results from numerous studies on the multiple photon reactions of organic molecules in solution. The initial investigations on the selectivities of radical fragmentation reactions from ground and excited states required the use of both pulsed and continuous wave laser techniques. Laser flash photolysis techniques were used to determine the $\alpha,\alpha$-dimethoxybenzyl radicals undergo fragmentation from the excited state with a quantum yield which is close to one. High intensity laser-jet photolysis was used to determine the selectivities for the excited state fragmentation of unsymmetrically substituted $\alpha,\alpha$-dialkoxybenzyl. It was found that the excited radicals show no selectivity upon fragmentation whereas the ground state radical fragmentations are governed by the thermodynamic stability of the radical products. Lack of a suitable method for the production of semi-preparative amounts of multiple photon reaction products in our own laboratory led us to develop a new technique which utilizes pulsed lasers. By irradiating small droplets of solution with the focused output from a pulse laser we were able to induce multiple photon reactions with efficiencies which are comparable to the laser-jet technique. A direct comparison was made for the case of diphenylmethyl radicals in carbon tetrachloride and methanol. This method, dubbed laser-drop photolysis, was used, along with laser-flash photolysis techniques and conventional lamp irradiations, to investigate and compare the chemistry for several transient species from both the ground and excited states. A number of unique reaction pathways have been found to occur from the excited states of the transient intermediates. For example, ground state 1,1-diphenylethoxyl radicals undergo a neophyl-like rearrangement to yield 1-phenoxy-1-phenylethyl radicals. From the excited state this radical undergoes $\beta$-scission, a process which does not occur from the ground state radical. Irradiation of small drops of liquid by the focused output from high powered pulse lasers results in their destruction in a manner similar to the ablative photodecomposition of organic polymers. We have investigated the dynamics of the drop explosion by taking Polaroid photographs with a time resolution of $\sim$20 ns by using a second pulsed laser as the flash for the camera. The destruction of the drops occurs in the $\mu$s time scale and a model has been proposed which is consistent with the dynamics of drop explosion. Further, pyrene has been used in attempts to probe the temperature increase inside the drop just prior to its explosion.

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45

Shu, Ronghua 1962. "Some novel organosilane reactions catalyzed by titanocenes." Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=35941.

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This thesis presents some novel organosilane reactions catalyzed by titanocenes.
Heterodehydrocoupling between silanes and phosphines has been accomplished with titanocenes, as catalysts. The reaction has the characteristics of high yield and high selectivity and can be carried out under mild conditions. Monophosphinosilanes and diphosphinosilanes can be selectively obtained from the reactions of secondary phosphines andsilanes. Primary phosphines react with primary silanes to produce 1,3,5-triphospha-2,4,6-trisilacyclohexanes. A two-catalytic-cycled mechanism is proposed with titanocene hydride as the key catalytic species.
Hydrosilation/hydrogenation of some aromatic N-heterocycles (namely pyridine, 3-picoline, 4-picoline, 3,5-lutidine, and quinoline) has been achieved with titanocene derivatives as catalysts. A variety of hydrosilated/hydrogenated products, either fully or partially saturated, may be produced depending on conditions. A reaction mechanism is proposed based on isolated and structurally characterized pyridine titanocene complexes, on the effects of substituent on the rates, and on H/D exchange studies. It is suggested that a key step in the hydrogenation/hydrosilation reaction is the formation of a mono-eta 1(N) complex between the pyridine ring and the titanocene silyl complex. It is proposed that the rate determining step is an intramolecular insertion of -N=C- into the Ti-Si bond. If the strong coordination or the intramolecular insertion is prohibited by either steric effects or electronic effects, or if the complex is of too high stability, no hydrogenation/hydrosilation product is obtained. Extensive H/D exchange at the 2- and 6-positions of the pyridine is attributed to a reversible ortho-metallation of pyridine in a Ti-H complex.
Cp2TiMe2 catalyzed hydrosilation/hydrogenation reactions of nicotinates, ethyl benzoate, and lactones have been studied. With ethyl nicotinate as the substrate, the hydrosilation occurs on the ring to give ethyl N-(methylphenylsilyl)-1,6-dihydronicotinate as the only product. No reaction at the ester group is observed. However, when the substrate is ethyl isonicotinate, ethyl 2-methylnicotinate or ethyl 6-methylnicotinate, the hydrosilation/hydrogenation only occurs at the ester groups and the carboalkoxy group is tranformed into either a silyl ether group or an alkyl group.
Copolymers can be produced from the titanocene catalyzed ring opening hydrosilation/hydrogenation reactions of lactones and PhMeSiH2. A key intermediate in these reactions, Cp[mu-(eta1:eta 5-C5H4)](THF)Ti(mu-H)TiCp 2, is isolated and well characterized by x-ray crystallography. The successful isolation and characterization of this product provides the first direct evidence to support the involvement of Cp2Ti in numerous Cp2TiMe2 catalyzed reactions in addition to correcting an earlier incorrect assignment of the structure of this frequently cited compound.

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46

Joensuu, Pekka Matias. "Development of catalytic stereoselective reductive aldol reactions." Thesis, University of Edinburgh, 2008. http://hdl.handle.net/1842/2576.

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The chemistry of enolates can be considered one of the cornerstone areas in organic chemistry. Regioselective generation of an enolate in the presence of several enolisable sites can often prove to be a difficult task. Discoveries in recent years have led to new areas of enolate formation in the presence of other carbonyl groups. These include reductive aldol chemistry where direct reductive aldol coupling of an alpha,beta - unsaturated carbonyl group in presence of a carbonyl electrophile enables often perfectly regioselective reactions to occur. This tandem conjugate reductionelectrophilic trapping process enables the reaction to be performed in a “one-pot” manner. The first examples of asymmetric copper-catalysed reductive aldol reactions have been developed for the formation of a range of beta-hydroxylactone products. A combination of Cu(OAc)2.H2O with different bisphosphine ligands catalyses these intramolecular reductive aldol reactions. TMDS (1,1,3,3-tetramethylhydrosiloxane) is used as a stoichiometric hydride source. The reaction proceeds with high relative stereocontrol (>19:1 dr), while absolute stereocontrol remains modest (up to 83% ee). The yields range from moderate to good. A continuous search for improved reaction conditions led to the discovery that cobalt-catalysed reductive aldol reactions have an advantage over the coppercatalysed reaction in the cases where 4-hydroxypiperidin-2-one products are formed. When Co(acac)2·H2O is used together with Et2Zn as the stoichiometric reductant, an increased substrate scope is observed while the diastereoselectivity of the reaction remains high. Yields are also remarkably higher compared to the results obtained with the copper catalyst. These reaction conditions are also used to perform intermolecular reductive aldol reactions between a range of alpha,beta-unsaturated amides and ketones. The reactions proceed readily with high diastereoselectivities (up to >19:1 syn:anti) and good yields. Asymmetric variants have been studied by the use of a chiral oxazolidine auxiliary. Although good selectivities have been obtained, this method currently suffers from the fact that the chiral auxiliary is difficult to cleave. Ni(acac)2 was also found to perform the intramolecular reductive aldol reaction. Et2Zn was again used as the stoichiometric reductant. The nickel-catalysed reaction increased the reaction scope still further. This time both beta-hydroxylactone and 4-hydroxypiperidin-2-one products were readily formed. The former proceeded with increased yields compared to those obtained with the copper catalyst, and, the latter with comparable results to those obtained with the cobalt catalyst.

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47

Carlsson, Magnus. "The inter- and intramolecular selectivity of the carbonate radical anion in its reactions with lignin and carbohydrates /." Doctoral thesis, Stockholm : Department of Chemistry - Nuclear Chemistry, Kungliga tekniska högskolan, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-257.

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48

Lee, Yoon Joo 1974. "Bismuth-mediated organometallic reactions in aqueous media." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=79029.

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Recently, organometallic reactions in aqueous media have received considerable attention in organic synthesis because of environmental and economical concerns and synthetic efficiency. In this connection, the synthetic utility of environmentally benign non-toxic bismuth metal for aqueous organometallic reactions is investigated. Bismuth metal activated by ammonium hydrogen fluoride can efficiently reduce a wide variety of alpha-halocarbonyl compounds in aqueous media to provide the corresponding dehalogenated reduction products in excellent yields. Zinc fluoride is also found to be effective in activating bismuth to mediate the crossed aldol type reactions of diverse alpha-bromocarbonyl compounds with aldehydes in aqueous media to afford the corresponding beta-hydroxycarbonyl compounds in moderate to high yields. The scope of bismuth-mediated aqueous organometallic reactions is successfully extended to the Reformatsky type reactions. The factors that affect the reactivity of these reactions are examined and plausible reaction mechanisms are proposed.

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49

Ma, Ruoyu. "Chiral NHC-Au(I) Catalyzed Enantioselective Reactions." Miami University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=miami1585432603722902.

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50

Shadrick, Melanie. "Effect of C-7,8 di-Picoloyl in Sialylation Reactions." Thesis, Southern Illinois University at Edwardsville, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10808011.

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N-acetyl neuraminic acid is most common member of the sialic acid family. This unique monosaccharide is displayed at the terminal position of oligosaccharides in glycoproteins and glycolipids on outer surface of a cell membrane.

The biological features of N-acetyl neuraminic acid involve cell-cell interactions in immunogenesis, as well as pathogens attacks, and overexpression in cancer cells.

The synthesis of sialic acid containing glycoconjugates is essential for a better understating of their biological function, as well as for the design of therapeutics. In addition, to the limitations of the enzymatic approach, chemical synthesis of these glycosidic linkages offer the opportunity to large scale isolation of common as well as uncommon oligosaccharides.

However, the stereocontrolled synthesis of sialic acid containing glycoconjugates is undoubtedly one of the most challenging research goals in the carbohydrate synthetic field. In particular, little is known on the effect of O-protecting groups in sialylation reactions. Recently we proved that a picoloyl group at C-4 can indeed favor an alpha sialylation if in the presence of an excess of triflic acid. Excellent stereoselectivities and yields were obtained with a wide range of galactosyl acceptors.

As a natural evolution of this finding, we decided to investigate the effect of picoloyl at other positions, as well stereoselectivities and yield in sialylations when di-picoloylated sialic acid donors are used.

Herein we report a systematic investigation of the regioselective introduction of picoloyl groups as well as the synthesis of a 7,8 di-picoloylated donor. The latter, when tested in sialylation reactions, gave exceptionally high yields and stereoselectivities.

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