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The Bucherer-Bergs reaction is a classical multi-component reaction that yields hydantoins, which can be hydrolysed to afford α-amino acids. Hydantoins have many uses in modern organic synthesis, and this moiety has been included in a number of therapeutic agents, which have a wide range of biological activities. Herein, we report a mild synthesis of 5- and 5,5-substituted hydantoins from α-aminonitriles using Hünig’s base and carbon dioxide. This reaction can be performed in excellent yields, using a variety of organic solvents and is applicable to a range of substrates. In an extension to the above methodology, a one-pot Lewis acid-catalysed synthesis of hydantoins from ketones has also been developed and optimised in organic media. This reaction can be performed in excellent yields and is suitable for the synthesis of 5- and 5,5-substituted hydantoins.

<p>This thesis describes the use of 2H-azirines as reactivesubstrates in Lewis acid catalysed nucleophilic additions andin the Diels-Alder reaction.A number of carbon nucleophiles have been added to aseries of 2H-azirines in the presence and absence ofBF3·Et2O. 3-(2-Naphthyl)-2H-azirine has been used as amodel substrate in the enantioselective addition oforganolithium reagents to an 2H-azirine.A selection of Lewis acids has been screened for theirpossible use in the normal electron demand Diels-Alder reactionbetween 3-alkyl-, 3-aryl-, and 3- carboxyl-2H-azirines and avariety of dienes. Lewis acid activation was found to shortenreaction times and facilitate lower reaction temperatures.These cycloadditions proceeded with endo selectivity providinga single diastereoisomeric product.DFT calculations of Lewis acid activated 2H-azirineshave been carried out.</p><p><b>Keywords:</b>2H-azirines, Lewis acid activation, chiralligands, organolithium reagents, Diels-Alder reactions,DFT-calculations</p>

Edible potatoes originated in the Andes and were brought to Europe in the 16th century. Their introduction spurred both the European population growth and economic development. Being the world's fourth-largest food crop, potatoes continue to shape the global economy and world history. Glycoalkaloids are natural insect deterrents generated by potatoes, and are known for their toxic effects as well as potential medicinal utilities. Demissidine, the aglycone of the primary glycoalkaloids, represents one major Solanum alkaloid. Its unique indolizidine framework presents a challenging synthetic target in organic chemistry. Our synthesis of demissidine starts from readily available epiandrosterone and takes advantage of a Lewis acid-mediated fragmentation of a γ-silyloxy-β-hydroxy-α-diazoester; the D-ring of a diazo ester derivative of epiandrosterone was efficiently ruptured to provide an aldehyde tethered ynoate product. In combination with a subsequent azomethine ylide 1,3-dipolar cycloaddition and a transition metal catalyzed oxidation/reduction, the core indolizidine framework of demissidine was successfully prepared in a stereoselective manner. In addition, the syntheses of two amino acids, 5-methylenepipecolic acid and (5S)-5-methylpipecolic acid were explored; they are used for the installation of the α-oriented C25 methyl group on demissidine. The successful preparation of demissidine was supported by NMR analysis of the synthetic compound in comparison with a natural sample. As an efficient and stereoselective synthesis, our efforts toward demissidine illuminate a strategy to indolizidine frameworks that could be applied in the preparation of other polycyclic amine natural products.

O objetivo deste trabalho foi investigar o uso de NbCl5 como ácido de Lewis em síntese orgânica (reações de abertura de epóxidos, reações de Diels-Alder e substituição eletrofílica de ciclo-enonas no anel furano e em reações de formação de beta-cloro-enonas e beta-etóxi-enonas a partir de beta-dicetonas e seus derivados acetilados. O comportamento de vários epóxidos quando tratados com NbCl5 foi estudado. Em geral verificou-se que os epóxidos estudados reagem rapidamente com NbCl5, levando geralmente à formação de mais de um produto (cloridrinas, 1,2-dióis, produtos contendo resíduos de solvente, como também produtos de rearranjo foram obtidos). Foi realizado um estudo detalhado verificando o efeito da temperatura (t.a., 0ºC ou -78ºC) e da concentração molar de NbCl5 nessas reações, com relação ao tempo e rendimento das reações, e à composição dos produtos. Reações entre diferentes ciclo-enonas (dienófilos de baixa reatividade) com ciclopentadieno e furanos (dienos) foram realizadas na presença de NbCl5. As reações mostraram que o NbCl5 é um bom ácido de Lewis para ativar reações de Diels-Alder ou substituição eletrofílica do hidrogênio pela ciclo-enona no anel furano. O produto de Diels-Alder foi obtido apenas na reação entre a ciclo-hexenona e o dieno mais reativo (ciclopentadieno). Dienos menos reativos, furano e 2-metil-furano levaram à formação de produtos de substituição eletrofílica do hidrogênio pela ciclo-enona no anel furano. beta-Dicetonas e seus derivados acetilados foram convenientemente transformados em beta-cloro-enonas e beta-etóxi-enonas pelo tratamento com NbCl5, em uma única etapa e em bons rendimentos. Observamos que quando as reações são realizadas em Et2O ou CH2Cl2 como solventes, apenas beta-cloro-enonas são formadas. Contudo, usando EtOAc como solvente, os resultados dependem da estrutura do substrato: substratos alfa-metilados formam exclusivamente beta-cloro-enonas (como nos outros solventes), enquanto os outros substratos levam à formação de beta-etóxi-enonas ou de misturas de beta-cloro-enonas e beta-etóxi-enonas. / The aim of this work was to investigate the use of NbCl5 as Lewis acid in organic synthesis (opening of epoxide rings, Diels-Alder and electrophilic substitution of cycloenones in furan ring reactions and in the formation of beta-chloroenones and beta-ethoxyenones from beta-diketones and the corresponding acetylated derivatives. The behaviour of several epoxides when treated with NbCl5 was studied. In general it was verified that the studied epoxides react rapidly with NbCl5, giving, in most cases, more than one product (chlorohydrins, 1,2-diols, products containing solvent residues as well as rearrangement products were obtained). A detailed study was performed to verify the effect of the temperature (rt, 0ºC or -78ºC) and of the NbCl5 molar concentration in the composition of the products, yield and time required for the reactions. Reactions between different cycloenones (dienophiles of low reactivity) with cyclopentadiene and furans (dienes) were performed in the presence of NbCl5. The reactions showed that NbCl5 is a good Lewis acid for Diels-Alder or electrophilic substitution of the hydrogen by the cycloenone system in furan ring. The Diels-Alder product was obtained only in reaction between the cyclohexenone and the highly reactive diene (cyclopentadiene). Less reactive dienes such as furan and 2-methylfuran gave electrophilic substitution of hydrogen by the cycloenone system in the furan ring. beta-Diketones and the corresponding acetylated derivatives were conveniently transformed in beta-chloroenones or beta-ethoxyenones by treatment with NbCl5, in one step and in good yields. When the reactions were carried out with Et2O or CH2Cl2 as solvents, only beta-chloroenones were obtained. However, with EtOAc as solvent, the results depend on the structure of the substrate: alpha-methylated substrates gave exclusively beta-chloroenones (as in other solvents), while the other substrates gave beta-ethoxyenones or mixtures of beta-ethoxyenones and beta-chloroenones.

Cette thèse a pour but d’étudier et d’approfondir les connaissances actuelles dans le domaine de la chimie des silyliums. Ces espèces cationiques semblables aux carbocations sont dotées d’une forte réactivité même vis-à-vis d’espèces très peu nucléophiles, ce qui leur confère des propriétés remarquables en tant qu’acide de Lewis. Les objectifs de cette thèse relèvent d’une tentative de dompter cette grande réactivité, via des méthodes de stabilisation du silylium, en conservant un bon compromis réactivité/stabilité. Un second axe de recherche envisagé est a visé d’application de ces silyliums en catalyse asymétrique et pour cela différents modèles ont été étudiés. Pour cela, l'introduction d'une chiralité centrée sur le silicium ou l'utilisation d'anion chiraux ont été étudiés. / The main objective of this thesis was to develop a better understanding of the silylium chemistry. These cationic three-coordinate silicon species similar to carbeniums are extremely reactive against any nucleophile and the extraordinarily high avidity of these cationic species for electron density make them remarkable Lewis acids. In this context, our aim during this thesis was to tame the reactivity of silyliums by means of introducing stabilisation at the cationic silicon center while preserving most of its reactivity. The study of new systems may provide informations on the way to find the best reactivity/stability compromise. Another part of this work was to focus on chirality in this stabilized silyliums to allow future asymmetric catalysis applications and the introduction of silicon-centered chirality but also chiral anions were probed.

Many commercialized medicinal compounds are analogs of chemicals isolated from sources found in nature (also called natural products). However, the natural sources of these chemicals, such as plants, fungi, or insects, only offer small quantities of these bioactive agents. Thus, it is typically desirable to find ways to synthesize these products and their analogs in large quantities using cost-effective methods that also minimize the impact on the environment. It is also important to develop strategies that expedite the process of modifying the natural products, which allows medicinal chemists to determine which functional groups are enhancing or deleterious to the bioactivity. In the Brewer lab, I have investigated organic reactions and methodologies with this aim - to find ways to efficiently break and form carbon-carbon bonds, and to utilize these reactions in the total synthesis of structurally related natural products. The total synthesis of natural products is often used to showcase a methodology's utility by applying it in a more complex structure. The Lewis acid-promoted fragmentation of γ-silyloxy-β-hydroxy-α-diazo esters to provide tethered aldehyde ynoates was discovered and developed in the Brewer lab. This methodology was extended to bicyclic systems, in which the ring-fusion bond fragmented as a way to afford 10-membered ring ynones and ynolides, which are traditionally challenging to synthesize. This work will exhibit how the fragmentation reaction that provided 10-membered ynolides has the potential to lend itself to the synthesis of several structurally related, bioactive natural products via a divergent total synthesis strategy. In addition, this dissertation will describe our discovery that modifying the diazo carbonyl precursor to a β-hydroxy-α-diazo ketone changes the course of the Lewis acid-promoted reaction. Rather than a fragmentation sequence, the compound is converted to a vinyl cation, which undergoes a rearrangement then a C-H insertion of a second vinyl cation intermediate. This transition metal-free rearrangement/C-H insertion reaction provided cyclopentenone products. The migratory aptitudes of non-equivalent substituents in the cationic rearrangement step will also be discussed. Finally, the disparate reactivities of vinyl cations derived from diazo ketone, diazo ester, and diazo amide precursors will be detailed from an experimental and computational perspective. The results underscore the fact that this rearrangement and C-H insertion reaction may eventually be an effective way to prepare complex cyclopentyl-containing structures, which are common motifs in biologically active natural products.

This thesis deals with the preparation and use of chiralbispyridylamides as ligands in metal-catalyzed asymmetricreactions. The compounds were prepared by amide formation usingdifferent coupling reagents. Bispyridylamides havingsubstituents in the 4- or 6- positions of the pyridine ringswere prepared by functional group interconversion of the 4- or6- halopyridine derivatives. These synthetic approaches provedto be useful for various types of chiral backbones. Pseudo C2-symmetric bispyridylamides were also synthesizedby means of stepwise amide formation. The compounds were used as ligands in themicrowave-accelerated Mocatalyzed asymmetric allylic alkylationreaction. Ligands having ð-donating substituents in the4-positions of the pyridine rings gave rise to products withhigher branched to linear ratio. The catalytic reaction, whichproved to be rather general for allylic carbonates with anaromatic substituent, was used as the key step in thepreparation of (R)-baclofen. The Mo-bispyridylamide catalystprecursor was studied by NMR spectroscopy. Bispyridylamide complexes of metal alkoxides were alsoevaluated in the asymmetric addition of cyanide to aldehydesand the metal complexes involved were studied by NMRspectroscopy and X-ray crystallography. Chiral diamines wereused as additives to study the ring opening of cyclohexeneoxide with azide, catalyzed by Zr(IV)-bispyridylamidecomplexes. Various bispyridylamides were attached to solid supports oforganic or inorganic nature. The solid-supported ligands wereused in Mo-catalyzed asymmetric allylic alkylation reactionsand in the asymmetric addition of cyanide to benzaldehyde. Keywords:asymmetric catalysis, chiral ligand, pyridine,amide, allylic alkylation, enantioselective, cyanation,ring-opening, chiral Lewis acid.

The recognition and capture of fluoride, cyanide and azide anions is attracting great deal of attention due to the negative effects of these anions on the environment and on human health. One of common methods used for the recognition and capture of these anions is based on triarylboranes, the Lewis acidity of which can be enhanced via variation the steric and electronic properties of the boron substituents. This dissertation is dedicated to the synthesis of novel boron-based anion receptors that, for the most part, feature an onium group bound to one of the aryl substituents. The presence of this group is shown to increase the anion affinity of the boron center via Coulombic effects. Another interesting effect is observed when the onium group is juxtaposed with the boron atom. This is for example the case of naphthalene-based compounds bearing a dimesitylboryl moiety at one of the peri-position and a sulfonium or telluronium unit at the other peri position. Fluoride anion complexation studies with these sulfonium or telluronium boranes, show that the boron-bound fluoride anion is further stabilized by formation of a B-F->Te/S bridge involving a lp(F)->sigma*(Te/S-C) donor acceptor interaction. Some of the sulfonium boranes investigated have been shown to efficiently capture fluoride anions from wet methanolic solutions. The resulting fluoride/sulfonium borane adducts can be triggered to release a "naked" fluoride equivalent in organic solution and thus show promise as new reagents for nucleophilic fluorination chemistry. Interestingly, the telluronium systems show a greater fluoride anion affinity than their sulfonium analogs. This increase is assigned to the greater spatial and energetic accessibility of the sigma* orbital on the tellurium atom which favors the formation of a strong B-F->Te interaction. This dissertation is concluded by an investigation of the Lewis acidic properties of B(C6Cl5)3. This borane, which has been reported to be non-Lewis acidic by other researchers, is found by us to bind fluoride, azide and cyanide anions in dichloromethane with large binding constants. This borane is also reactive toward neutral Lewis bases, such as p-dimethylaminopyridine, in organic solvents.

This thesis describes a number of synthetic approaches for obtaining chiral, enantiomerically pure natural products, in particular some semiochemicals. This has been accomplished by using various strategies; by starting from compounds from the chiral pool, by using chiral auxiliaries, via enzymatic resolutions or by chemical asymmetric synthesis. Hence, the sexual pheromone of Microdiprion pallipes, a propanoate ester of one or several isomers of 3,7,11-trimethyltridecan-2-ol, was synthesised, both as a mixture of all isomers and as the sixteen pure, individual stereoisomers. These compounds were obtained by joining different enantiopure building blocks stemming from the chiral pool. When compared with some synthetic blends, both the propanoate esters of the stereoisomeric erythro-3,7,11-trimethyltridecan-2-ols originally found in the extract from the female of M. pallipes, surprisingly, showed lower activities in biological studies. Indeed, the propanoates of two threo-isomers gave significantly higher responses in biological tests, than did the propanoates of the two natural erythro-ones. Because the synthetic strategy used earlier was not very efficient for the preparation of the threo-isomers of 3,7,11-trimethyltridecan-2-ol, we were encouraged to look for alternative synthetic approaches. The new synthetic strategy chosen led us to two key synthetic building blocks, an O-protected derivative of (2S,3S)-3-methyl-4-(phenylsulfonyl)butan-2-ol butanol and (3R,7R)-1-iodo-3,7-dimethylnonane. Deprotonation of the former followed by alkylation with the latter should give a compound with the desired carbon skeleton. For efficient preparation of the first building block, we developed a new diastereoselective addition reaction of dialkylzincs to some chiral aldehydes, the products of which were diastereomerically enriched 1,2-dialkyl-alkanols. Using this method, each enantiomer of the desired building block was obtained via efficient diastereoselective addition of dimethylzinc to each enantiomer of a 2-methylaldehyde. The resulting product, a diastereomerically and enantiomerically highly enriched 3-methyl-2-alkanol was further purified by enzyme catalysed acylation followed by some functional group interconversions. The second building block was prepared via convergent multistep synthesis, starting from a single, enantiomerically pure compound, (R)-2-methylsuccinic acid 4-t-butyl ester, derived from the chiral pool. The two enantiomerically pure building blocks, so obtained, were coupled together. Some additional functional group manipulations of the product produced furnished the desired isomer, which had shown the highest activity in field tests of the M. pallipes, namely the propanoate ester of (2S,3R,7R,11R)-3,7,11-trimethyltridecan-2-ol. This thesis describes a number of synthetic approaches for obtaining chiral, enantiomerically pure natural products, in particular some semiochemicals. This has been accomplished by using various strategies; by starting from compounds from the chiral pool, by using chiral auxiliaries, via enzymatic resolutions or by chemical asymmetric synthesis. Hence, the sexual pheromone of Microdiprion pallipes, a propanoate ester of one or several isomers of 3,7,11-trimethyltridecan-2-ol, was synthesised, both as a mixture of all isomers and as the sixteen pure, individual stereoisomers. These compounds were obtained by joining different enantiopure building blocks stemming from the chiral pool. When compared with some synthetic blends, both the propanoate esters of the stereoisomeric erythro-3,7,11-trimethyltridecan-2-ols originally found in the extract from the female of M. pallipes, surprisingly, showed lower activities in biological studies. Indeed, the propanoates of two threo-isomers gave significantly higher responses in biological tests, than did the propanoates of the two natural erythro-ones. Because the synthetic strategy used earlier was not very efficient for the preparation of the threo-isomers of 3,7,11-trimethyltridecan-2-ol, we were encouraged to look for alternative synthetic approaches. The new synthetic strategy chosen led us to two key synthetic building blocks, an O-protected derivative of (2S,3S)-3-methyl-4-(phenylsulfonyl)butan-2-ol butanol and (3R,7R)-1-iodo-3,7-dimethylnonane. Deprotonation of the former followed by alkylation with the latter should give a compound with the desired carbon skeleton. For efficient preparation of the first building block, we developed a new diastereoselective addition reaction of dialkylzincs to some chiral aldehydes, the products of which were diastereomerically enriched 1,2-dialkyl-alkanols. Using this method, each enantiomer of the desired building block was obtained via efficient diastereoselective addition of dimethylzinc to each enantiomer of a 2-methylaldehyde. The resulting product, a diastereomerically and enantiomerically highly enriched 3-methyl-2-alkanol was further purified by enzyme catalysed acylation followed by some functional group interconversions. The second building block was prepared via convergent multistep synthesis, starting from a single, enantiomerically pure compound, (R)-2-methylsuccinic acid 4-t-butyl ester, derived from the chiral pool. The two enantiomerically pure building blocks, so obtained, were coupled together. Some additional functional group manipulations of the product produced furnished the desired isomer, which had shown the highest activity in field tests of the M. pallipes, namely the propanoate ester of (2S,3R,7R,11R)-3,7,11-trimethyltridecan-2-ol. This thesis describes a number of synthetic approaches for obtaining chiral, enantiomerically pure natural products, in particular some semiochemicals. This has been accomplished by using various strategies; by starting from compounds from the chiral pool, by using chiral auxiliaries, via enzymatic resolutions or by chemical asymmetric synthesis. Hence, the sexual pheromone of Microdiprion pallipes, a propanoate ester of one or several isomers of 3,7,11-trimethyltridecan-2-ol, was synthesised, both as a mixture of all isomers and as the sixteen pure, individual stereoisomers. These compounds were obtained by joining different enantiopure building blocks stemming from the chiral pool. When compared with some synthetic blends, both the propanoate esters of the stereoisomeric erythro-3,7,11-trimethyltridecan-2-ols originally found in the extract from the female of M. pallipes, surprisingly, showed lower activities in biological studies. Indeed, the propanoates of two threo-isomers gave significantly higher responses in biological tests, than did the propanoates of the two natural erythro-ones. Because the synthetic strategy used earlier was not very efficient for the preparation of the threo-isomers of 3,7,11-trimethyltridecan-2-ol, we were encouraged to look for alternative synthetic approaches. The new synthetic strategy chosen led us to two key synthetic building blocks, an O-protected derivative of (2S,3S)-3-methyl-4-(phenylsulfonyl)butan-2-ol butanol and (3R,7R)-1-iodo-3,7-dimethylnonane. Deprotonation of the former followed by alkylation with the latter should give a compound with the desired carbon skeleton. For efficient preparation of the first building block, we developed a new diastereoselective addition reaction of dialkylzincs to some chiral aldehydes, the products of which were diastereomerically enriched 1,2-dialkyl-alkanols. Using this method, each enantiomer of the desired building block was obtained via efficient diastereoselective addition of dimethylzinc to each enantiomer of a 2-methylaldehyde. The resulting product, a diastereomerically and enantiomerically highly enriched 3-methyl-2-alkanol was further purified by enzyme catalysed acylation followed by some functional group interconversions. The second building block was prepared via convergent multistep synthesis, starting from a single, enantiomerically pure compound, (R)-2-methylsuccinic acid 4-t-butyl ester, derived from the chiral pool. The two enantiomerically pure building blocks, so obtained, were coupled together. Some additional functional group manipulations of the product produced furnished the desired isomer, which had shown the highest activity in field tests of the M. pallipes, namely the propanoate ester of (2S,3R,7R,11R)-3,7,11-trimethyltridecan-2-ol. / QC 20101026