The mechanism of organothiol (OT) binding to gold has remained controversial for decades. There are three mechanisms proposed for OT binding to gold surfaces. The first is the radical pathway in which the sulfur-bound hydrogen atoms (RS-H) are released as hydrogen atoms which eventually converted into hydrogen gas. Second is the deprotonation pathway in which the sulfur-bound hydrogen atoms leave as protons. Third is direct adsorption in which the RS-H bonds remain intact on the gold surface. This study demonstrates a combined pH and surface enhanced Raman spectroscopic study of organothiol binding to citrate- and borohydride-reduced gold nanoparticles (AuNPs) in polar (water), moderately polar (dichloromethane), and nonpolar (toluene,hexane) solvents. Thiol deprotonation provides a unified pathway for OT binding to AuNPs regardless of solvent polarity of the ligand binding solutions. This work should contribute to resolve the long-standing debate on the fate of the sulfur-bound hydrogen of organothiols self-assembled on gold.

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Detailed mechanistic studies on the palladium-catalyzed direct arylation of pyridine N-oxides are presented. The order of each reaction component is determined to provide a general mechanistic picture. The C-H bond cleaving step is examined in further detail through computational studies, and the calculated results are in support of an inner-sphere concerted metallation-deprotonation (CMD) pathway. Competition experiments were conducted using N-oxides of varying electronic characters, and results revealed an enhancement of rate when using a more electron-deficient species which is in support of a CMD transition state. The effect of base on reaction rate was also examined and it was found that a carboxylate base was required for the reaction to proceed. This led to the conclusion that Pd(OAc)2 plays a pivotal role in the reaction mechanism as more than merely a pre-catalyst, but as a source of acetate base required for the C-H bond cleavage step.

New processes that leads to formation of new carbon-carbon bond (the Michael reaction, the Mannich reaction and alkylation reaction) or carbon-heteroatom bond (á-halogenation, á-hydroxylation and á-amination) on bridged bicyclic ketones such as tropinone and TBON were investigated, utilizing LDA in the deprotonation step. All reactions, in which new carbon-heteroatom bond is formed, were not successful either due to low selectivity and/or yields. In case of new carbon-carbon bond forming processes, careful choice of electrophile (electrophile having the ester group in á-position to leaving group), allows for alkylation of tropinone with moderate yield and good selectivity. Application of new conditions to the aldol reaction of TBON and tropinone (e.g. MgI2 catalyzed aldol reaction), gave new aldol products that were not detected from the lithium enolate chemistry of these ketones. Modification of reaction conditions in case of MgI2 catalyzed aldol reaction provides, in a one pot process, bis-aldol product from TBON in good yield and high selectivity, as a single diastereoisomer. Finally, TBON is used as a suitable scaffold for the synthesis of thiacocaine. The first known synthesis of racemic thiacocaine is presented, via deprotonation of TBON with LDA, as a key step.

Detailed mechanistic studies on the palladium-catalyzed direct arylation of pyridine N-oxides are presented. The order of each reaction component is determined to provide a general mechanistic picture. The C-H bond cleaving step is examined in further detail through computational studies, and the calculated results are in support of an inner-sphere concerted metallation-deprotonation (CMD) pathway. Competition experiments were conducted using N-oxides of varying electronic characters, and results revealed an enhancement of rate when using a more electron-deficient species which is in support of a CMD transition state. The effect of base on reaction rate was also examined and it was found that a carboxylate base was required for the reaction to proceed. This led to the conclusion that Pd(OAc)2 plays a pivotal role in the reaction mechanism as more than merely a pre-catalyst, but as a source of acetate base required for the C-H bond cleavage step.

New processes that leads to formation of new carbon-carbon bond (the Michael reaction, the Mannich reaction and alkylation reaction) or carbon-heteroatom bond (á-halogenation, á-hydroxylation and á-amination) on bridged bicyclic ketones such as tropinone and TBON were investigated, utilizing LDA in the deprotonation step. All reactions, in which new carbon-heteroatom bond is formed, were not successful either due to low selectivity and/or yields. In case of new carbon-carbon bond forming processes, careful choice of electrophile (electrophile having the ester group in á-position to leaving group), allows for alkylation of tropinone with moderate yield and good selectivity. Application of new conditions to the aldol reaction of TBON and tropinone (e.g. MgI2 catalyzed aldol reaction), gave new aldol products that were not detected from the lithium enolate chemistry of these ketones. Modification of reaction conditions in case of MgI2 catalyzed aldol reaction provides, in a one pot process, bis-aldol product from TBON in good yield and high selectivity, as a single diastereoisomer. Finally, TBON is used as a suitable scaffold for the synthesis of thiacocaine. The first known synthesis of racemic thiacocaine is presented, via deprotonation of TBON with LDA, as a key step.

Detailed mechanistic studies on the palladium-catalyzed direct arylation of pyridine N-oxides are presented. The order of each reaction component is determined to provide a general mechanistic picture. The C-H bond cleaving step is examined in further detail through computational studies, and the calculated results are in support of an inner-sphere concerted metallation-deprotonation (CMD) pathway. Competition experiments were conducted using N-oxides of varying electronic characters, and results revealed an enhancement of rate when using a more electron-deficient species which is in support of a CMD transition state. The effect of base on reaction rate was also examined and it was found that a carboxylate base was required for the reaction to proceed. This led to the conclusion that Pd(OAc)2 plays a pivotal role in the reaction mechanism as more than merely a pre-catalyst, but as a source of acetate base required for the C-H bond cleavage step.

Detailed mechanistic studies on the palladium-catalyzed direct arylation of pyridine N-oxides are presented. The order of each reaction component is determined to provide a general mechanistic picture. The C-H bond cleaving step is examined in further detail through computational studies, and the calculated results are in support of an inner-sphere concerted metallation-deprotonation (CMD) pathway. Competition experiments were conducted using N-oxides of varying electronic characters, and results revealed an enhancement of rate when using a more electron-deficient species which is in support of a CMD transition state. The effect of base on reaction rate was also examined and it was found that a carboxylate base was required for the reaction to proceed. This led to the conclusion that Pd(OAc)2 plays a pivotal role in the reaction mechanism as more than merely a pre-catalyst, but as a source of acetate base required for the C-H bond cleavage step.

Le développement de nouvelles méthodologies énantiosélectives organocatalysées est au centre des projets de cette thèse. Nous avons plus particulièrement considéré le potentiel de "paires d'ions coopératifs" chirales possédant une partie ammonium dérivée des alcaloïdes de quinquina et une partie anionique à caractère nucléophile permettant d'activer un réactif. Dans un premier temps, nous avons employé un amidure d'ammonium chiral (généré in situ par réaction entre un amide N-silylé et un phénolate de quininium) comme base de Brønsted délivrée en quantité catalytiques en deux réactions distinctes. Initialement, cette stratégie nous a permis de mettre au point un procédé de désymétrisation de cétones prochirales par déprotonation éniantosélective. Bien que les excès énantiométriques obtenus restent modestes, notre approche constitue la première version organocatalysée. Puis, nous avons pu développer avec succès une nouvelle réaction d'aldolisation directe vinylogue énantiosélective de (5H)-furan-2-ones avec de bons rendements et diastérosélectivités anti et des excès énantiométriques allant jusqu'à 94 %. Dans un second temps, nous avons décrit deux nouveaux cycles catalytiques de protonation énantiosélective d'énolates masqués. Tout d'abord, l'utilisation d'hydrogénocarbonate de potassium et d'une amine chirale a conduit à l'obtention de cétones énantioenrichies α-substituées avec des excès énantiométriques allant jusqu'à 93 % à partir des trifluoacétates d'énols correspondants. Puis, les propriétés de base de Lewis de nos phénolates d'ammoniums quaternaires chiraux ont été valorisés lors de la protonation énantiosélectives d'éthers d'énols silylés en présence de phénols. / This work deals with the development of new asymetric organocatalyzed methodologies. More particularly we were focused on using "cooperative chiral ion pairs" having an ammonium moiety derived from cinchona alkaloids and an anionic moiety with nucleophilic properties able to activate a reagent.Firstly, we used an in situ generated chiral ammonium amide (from the combination of an aminosilane and a quininium aryloxide) as a Brønsted base in two distinct reactions. Initially, this strategy was applied to an organocatalyzed desymmetrization of prochiral ketones by enantioselective deprotonation. Despite modest enantiometric excesses, this report constitutes the first example of an enantioselective orgonacatalyc approach. Then, an anti-selective direct vinylogous asymmetric aldol reaction of (5H)-furan-2-ones was achieved in good yields and enantioselectivities up to 94%.Secondly, we described two new catalytic cycles for the enantioselective protonation of latent enolates. By means of cinchona alkaloids and hydrogenocarbonates, enantioenriched α-substituted ketones were obtained with good enantiometric excesses up to 93% starting from the corresponding enol trifluoacetates. Finally, the nucleophilic properties of our ammonium phenoxide catalysts prompted us to develop an enantioselective protonation reaction of silyl enol ethers in the presence of phenol as achiral proton source.