Organometallic catalysis has attracted significant interest from both industry and academia due to its wide applications in organic synthetic transformations. Example of such transformations include the reaction of a zinc carbenoid with olefins to form cyclopropanes. The first project is a computational study using both density functional and correlated wavefunction methods of the reaction between ethylene and model zinc carbenoid, nitrenoid and oxenoid complexes (L-Zn-E-X, E = CH2, NH or O, L = X = I or Cl). It was shown that cyclopropanation of ethylene with IZnCH2I and aziridination of ethylene with IZnNHI proceed via a single-step mechanism with an asynchronous transition state. The reaction barrier for the aziridination with IZnNHI is lower than that of cyclopropanation. Changing the leaving group of IZnNHI from I to Cl, changes the mechanism of the aziridination reaction to a two-step pathway. The calculation results from the epoxidation with IZnOI and ClZnOCl oxenoids suggest a two-step mechanism for both oxenoids. Another important example of organometallic catalysis is the formation of alkyl arenes from arenes and olefins using transition metal catalysis (olefin hydroarylation). We studied with DFT methods the mechanism of a novel Rh catalyst (FlDAB)Rh(TFA)(η2–C2H4) [FlDAB = N,N’ -bis(pentafluorophenyl)-2,3-dimethyl-1,4-diaza-1,3-butadiene; TFA = trifluoroacetate] that converts benzene, ethylene and air-recyclable Cu(II) oxidants to styrene. Possible mechanisms are discussed.

Olefin metathesis is a powerful tool for the making and breaking of carbon-carbon double bonds. Among well-defined homogenous catalysts for olefin metathesis, ruthenium-based alkylidenes stand out for their robustness and relative ease-of-use. Synthesis of the most active Ru-based metathesis catalysts remains challenging, however, and there is continued interest in new and improved routes to alkylidene installation as metathesis begins to see wide uptake in industry. The first part of this thesis focuses on developing new routes to known catalysts. Magnesium carbenoids are investigated as a potential alkylidene source, and in the process a novel route to benzylmagnesium carbenoids is developed. Initially promising results showing ca. 40% conversion to first generation metathesis catalysts failed to lead to a viable high-yield route to Ru-alkylidenes. A high yield route to RuCl2(H2IMes)(py)4 (previously reported in low yields as a decomposition product of the third-generation Grubbs’ metathesis catalyst) is developed and this complex is investigated as a precursor to indenylidene-based catalysts. Although RuCl2(H2IMes)(py)4 is shown to be substitutionally labile, indenylidene installation could not be achieved. Finally, zinc aryloxides are investigated as an alternative to thallium and silver reagents for the installation of aryloxide ligands. Initial results indicate that zinc aryloxides are kinetically, though not thermodynamically, competent for the installation of the challenging aryloxide C6F5O- on the second-generation Hoveyda catalyst. The second part of this thesis concerns progress towards the development of a new low-valent catalyst platform. Initial experiments involving treating the second-generation Hoveyda catalyst with various reducing agents fail to produce low-valent alkylidenes, leading instead to decomposition of alkylidene. Drawing inspiration from early transition metal systems, the remainder of the second part focuses on alpha-hydride elimination from a RuII alkyl as a means of accessing low-valent alkylidenes. To this end, a novel benzylruthenium complex as well as bis-benzyl and mono-aryloxide derivatives are developed. While attempts to induce benzyl-to-benzyl hydride abstraction or intramolecular deprotonation of the benzyl ligand failed to produce alkylidenes, ligand-induced benzyl-to-aryloxide hydride abstraction appears to be successful, leading to the observation of a broad 1H NMR signal in the region characteristic for low-valent Ru-alkylidenes.

No description available.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / This work presents the synthesis and crystallographical study of indium organometallic compounds series in II and III oxidation states. Br2In(diox)2CH2Br and tetrahedral indium cluster, In4R4 [R = C(SiMe3)3], were adopted as starting materials of this work. We have made two different systematic studies: (a) reaction of Br2In(diox)2CH2Br with dialkylselenides R1SeR2 (R1 = CH3, R2 = CH2Ph; R1 = C2H5, R2 = CH2Ph; R1 = R2 = CH2Ph) and (b) reaction between the tetrahedral indium cluster and different chalcogenide donor ligands, such as PhEEPh (E = S, Se and Te), ArTeTeAr (Ar = CH3C6H4) and PhEBr (E = Se and Te), and haloforms as well, CHX3 (X = Cl, Br and I). The haloforms were applied as mild halogen donors. Br2In(diox)2CH2Br is obtained by the direct reaction between InBr and CH2Br2 in 1,4-dioxane. The Br3InCH2Se(CH3)CH2Ph (1), Br3InCH2Se(C2H5)CH2Ph (2) and Br3InCH2Se(CH2Ph)2 (3) derivatives are obtained by the reaction between Br2In(diox)2CH2Br and their own dialkylselenides. Tetrahedral indium cluster is obtained by the reaction between InBr and C(SiMe3)3·2THF in equivalent amounts. The new organoindium subhalides, R2In2Cl2 (4), R2In2Br2 (5), R2In2I2 (6), and the new indium(III) dimeric compounds as well, [RIn(SPh)2]2 (7), [RIn(SePh)2]2 (8), [RIn(TePh)2]2 (9) and [RIn(ArPh)2]2 (10), [RIn(Br)SePh]2 (11), [RIn(Br)TePh]2 (12), were obtained by the direct reaction of tetrahedral indium cluster and their respective halide or chalcogenide donors. / Este trabalho apresenta a síntese e o estudo cristalográfico de uma série de compostos organometálicos de índio nos estados de oxidação II e III. Os materiais de partida utilizados neste trabalho foram o Br2In(diox)2CH2Br e o cluster tetraédrico de índio, In4R4 [R = C(SiMe3)3]. Realizou-se dois tipos de estudos sistemáticos: (a) reação de Br2In(diox)2CH2Br com dialquilselenetos R1SeR2 (R1 = CH3, R2 = CH2Ph; R1 = C2H5, R2 = CH2Ph; R1 = R2 = CH2Ph) e (b) reação do cluster de índio com diferentes ligantes contendo calcogênios, como PhEEPh (E = S, Se e Te), ArTeTeAr (Ar = CH3C6H4) e PhEBr (E = Se e Te) e com halofórmios, CHX3 (X = Cl, Br e I). Os halofórmios foram utilizados como doadores de halogênio moderados. Br2In(diox)2CH2Br é obtido através da reação entre InBr e CH2Br2 em 1,4-dioxano. Os derivados Br3InCH2Se(CH3)CH2Ph (1), Br3InCH2Se(C2H5)CH2Ph (2) e Br3InCH2Se(CH2Ph)2 (3) são obtidos através da reação entre Br2In(diox)2CH2Br e seus respectivos dialquilselenetos. O cluster tetraédrico de índio é obtido a partir da reação de InBr e C(SiMe3)3·2THF em quantidades equivalentes. Os novos derivados de halogênio, R2In2Cl2 (4), R2In2Br2 (5), R2In2I2 (6), e os novos compostos diméricos de índio(III), [RIn(SPh)2]2 (7), [RIn(SePh)2]2 (8), [RIn(TePh)2]2 (9) e [RIn(ArPh)2]2 (10), [RIn(Br)SePh]2 (11), [RIn(Br)TePh]2 (12), foram obtidos através da reação direta do cluster de índio com seus respectivos doadores de halogênio ou calcogênio.

No description available.

No description available.

Carbenoides são intermediários altamente reativos que desempenham um papel fundamental em estratégias sintéticas modernas. Essas espécies são muito semelhantes aos carbenos no estado singleto, visto que possuem um caráter ambifílico e reagem por um mecanismo concertado, levando a produtos estereoespecíficos. Estudos preliminares demonstraram a versatilidade de um carbenoide misto de magnésio e lítio (ClCH2 MgCl·LiCl) na reação com diversos aldeídos aromáticos, alifáticos e heterocíclicos. Desta maneira, o objetivo deste trabalho foi estudar a quimiosseletividade de tal reagente e investigar a aplicação deste na síntese diasterosseletiva do (2S,3S)-N-Boc-3amino-1,2-epóxi-4-fenilbutano e seu diastereoisômero de configuração (2R,3S). Para a primeira parte do trabalho, selecionamos alguns aldeídos contendo grupos funcionais, tais como, ésteres, nitrilas, cetonas, amida, entre outros. De maneira geral, o carbenoide de magnésio mostrou-se muito eficiente e quimiosseletivo, levando a 14 cloridrinas funcionalizadas em bons rendimentos isolados, contudo, quando grupos doadores de elétrons estavam presentes na posição 4 do anel, o aldeído apresentou uma diminuição de reatividade e impossibilitou a obtenção do produto desejado. Por fim, estudos preliminares visando à preparação dos epóxidos de configuração (2S,3S) e (2R,3S) foram também realizados e os resultados são discutidos de forma detalhada no texto. / Carbenoids are a class of highly reactive intermediate compounds that play a key role in modern synthetic strategies. These species show a state very similar to that of singlet state carbenes since they have an ambiphilic character and react by a concerted mechanism, something that allows them to afford stereospecific products. Previous studies demonstrated the versatility of a mixed magnesium and lithium carbenoid (ClCH 2 MgCl·LiCl) in the reaction with a number of aromatic, aliphatic and heterocyclic aldehydes. In this way, the objective of this work was to study the chemoselectivity of such reagent and investigate its application in the diastereoselective synthesis of (2S,3S)-N-Boc-3-amino-1,2-epoxy-4-phenylbutane and its diastereoisomer of configuration (2R,3S). For the first part of the work we selected some aldehyde containing functional groups such as esters, nitriles, ketones and amide, among others. In summary, the magnesium carbenoid proved to be very efficient and chemoselective, leading to 14 functionalized chlorohydrins in good isolated yields. Nevertheless, when electron donating groups were present at the position 4 of the substrates ring, the resulting aldehyde showed a decrease in reactivity, which precluded us to obtain the desired product. Finally, preliminary studies aiming the preparation of the epoxides of configuration (2S,3S) and (2R,3S) were also investigated and the results are discussed in detail in the text.

This thesis is divided into four separate parts with amino alcohols as the common feature. The first part of the thesis describes the development of an efficient three-component approach to the synthesis of α-hydroxy-β-amino esters. Utilizing a highly diastereoselective Rh(II)-catalyzed 1,3-dipolar cycloaddition of carbonyl ylides to various aldimines, syn-α-hydroxy-β-amino esters are formed in high yields and excellent diastereoselectivities. An asymmetric version was also developed by employing chiral α-methylbenzyl imines as dipolarophiles yielding enantiomerically pure syn-α-hydroxy-β-amino esters. This methodology was also applied on a short asymmetric synthesis of the paclitaxel side-chain as well as in an asymmetric synthetic approach towards the proteasome inhibitor omuralide. Furthermore, the use of chiral Rh(II) carboxylates furnishes the syn-α-hydroxy-β-amino esters in moderate enantioselectivity (er up to 82:18), which indicates that the reaction proceeds via a metal-associated carbonyl ylide. The second part describes the development of a 1,3-dipolar cycloaddition reaction of azomethine ylides to aldehydes for the synthesis of α-amino-β-hydroxy esters. Different methods for the generation of the ylides, including Vedejs’ oxazole methology and an Ag(I)/phosphine-catalyzed approach have been evaluated. The best results were obtained with the Ag(I)/phosphine approach, which yielded the desired α-amino-β-hydroxy ester in 68% yield and 3.4:1 syn:anti-selectivity. The last two parts deals with the total synthesis of the amino alcohol-containing natural products D-erythro-sphingosine and (−)-stemoamide. The key transformation in the sphingosine synthesis is a cross-metathesis reaction for the assembly of the polar head group and the aliphatic chain. In the stemoamide synthesis, the key feature is an iodoboration/Negishi/RCM-sequence for the construction of the β,γ-unsaturated azepine core of stemoamide followed by a stereoselective bromolactonization/1,4-reduction strategy for the installation of the requisite C8-C9 trans-stereochemistry. / QC 20100820

The selective transformation of carbon-carbon and carbon-hydrogen bonds represents an attractive approach and rapidly developing frontier in synthesis. Benefits include step and atom economy, as well as the ubiquitous presence in organic molecules. Advances to this exciting realm of synthesis are described in this thesis with an emphasis on the development of catalytic, selective reactions under mild conditions. Additionally some applications of the methodologies are demonstrated. In Chapter 1, the first examples of inter-and intramolecular enantioselective conjugate alkenylations employing organostannanes are reported. A chiral, cationic Rh(I)-diene complex catalyzed the enantioselective conjugate addition of alkenylstannanes to benzylidene Meldrum’s acids in moderate enantiomeric ratios and yields. Notably, the cationic and anhydrous conditions required for the asymmetric alkenylation are complementary to existing protocols employing other alkenylmetals. In Chapter 2, a domino, one-pot formation of tetracyclic ketones from benzylidene Meldrum’s acids using Sc(OTf)3 via a [1,5]-hydride shift/cyclization/Friedel-Crafts acylation sequence is described. Respectable yields were obtained in accord with the ability to convert to the spiro-intermediate, and considering the formation of three new bonds: one C-H and two C-C bonds. An intriguing carbon-carbon bond cleavage was also serendipitously discovered as part of a competing reaction pathway. In Chapter 3, the pursuit of novel C-H bond transformations led to the development of non-carbonyl-stabilized rhodium carbenoid Csp3-H insertions. This methodology enabled the rapid synthesis of N-fused indolines and related complex heterocycles from N-aziridinylimines. By using a rhodium carboxamidate catalyst, competing processes were minimized and C-H insertions were found to proceed in moderate to high yields. Also disclosed is an expedient total synthesis of (±)-cryptaustoline, a dibenzopyrrocoline alkaloid, which highlights the methodology. In Chapter 4, the Lewis acid promoted substitution of Meldrum’s acid discovered during the course of the domino reaction was explored in detail. The protocol transforms unstrained quaternary and tertiary benzylic Csp3-Csp3 bonds into Csp3-X bonds (X = C, N, H) and has even shown to be advantageous with regards to synthetic utility over the use of alternative leaving groups for substitutions at quaternary benzylic centers. This reaction has a broad scope both in terms of suitable substrates and nucleophiles with good to excellent yields obtained (typically >90%).

The synthesis of cyclic allenes with eight or less skeletal C-atoms, known as highly strained organic compounds, has for the past decades attracted increasing interest. The first part of study describes an investigation aimed at the incorporation of an allene unit into a natural compound, being &amp / #945 / -pinene, by using &amp / #946 / -elimination method. The two double-bond isomers 310 and 299b were synthesized as key compounds. Treatment of 310 with t-BuOK resulted in the formation of ketone 308 and diene 313. For the formation of 308, the cyclic allene 300 was proposed as an intermediate. Treatment of 299b, with t-BuOK gave arise to the diene 313 and the dimerization product 322. On the basis of density-functional-theory (DFT) calculations on the allene 300 and the alkyne 320, the formation of the latter as the intermediate was excluded. In the second part of study, the stability of endo-carbene 304 was investigated. Previous studies indicated, during the formation of intermediate 264, no exo-carbene 330 structure could be optimized in its free carbene form. At this point, we were curious about the stability of endo-cyclopropylidene 304 not discussed before in literature. First, addition of bromofluorocarbene to anti-7-ethylbenzonorbornadiene (352) was aimed to isolate the endo-adduct 302b. However, no carbene addition reaction was observed caused by pyramidalization on double bond respect to the methoxy derivative, 363b. Therefore, the bromine was introduced to C-7 carbon atom. Treatment of 302a with MeLi in the presence of furan, gave furan adduct 306a confirmed the formation of allene 305a as a reactive intermediate. Theoretical calculations showed endo-carbene 304a was optimized in the free carbene form . However, it readily isomerizes to allene 305a afforded furan adduct 306a.