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  • 1.
    Fransson, Ann-Britt L.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Deracemization of Functionalized Alcohols via Combined Ruthenium and Enzyme Catalysis2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The major part of this thesis describes the synthesis of enantiopure alcohols and diols by combining ruthenium-catalyzed racemization or epimerization and lipase-catalyzed asymmetric transformations. A minor part of this thesis is focused on ruthenium-catalyzed redox reactions for transfer hydrogenation of 1,3-cycloalkanediketones.

    Kinetic resolution of racemic γ-hydroxy acid derivatives was performed via Pseudomonas cepacia lipase (PS-C)-catalyzed transesterification. γ-Hydroxy esters and γ-hydroxy amides were studied showing in higher selec-tivity and yields for the γ-hydroxy amides. The enzyme PS-C tolerates both variation in the chain length and different functionalities giving good to high enantioselectivity. Combining enzymatic kinetic resolution with a ruthenium-catalyzed racemization led to a dynamic kinetic resolution (DKR). The use of 2,4-dimethyl-3-pentanol as a hydrogen source to suppress ketone formation in the dynamic kinetic resolution increased the yields of the acetate product. The synthetic utility of this procedure was illustrated by the practical synthesis of the γ-lactone (R)-5-methyltetrahydrofuran-2-one.

    A distereoselective transformation of cis/trans-1,3-cyclohexandiol using Candida antarctica lipase B (CALB)-catalyzed transesterification was of interest. Desymmetrization of cis-1,3-cyclohexanediol to the (R-monoacetate was successfully accomplished. Enantiopure (R,R)-diacetate was obtained from the (R)-monoacetate in a DYKAT process at room tem-perature. Metal- and enzyme-catalyzed transformation of cis/trans-1,3-cyclohexanediol using PS-C, gives a high diastereoselectivity for cis-diacetate. The (S)-mono-acetate was obtained from cis-diacetate by CALB-catalyzed hydrolysis. In addition, it was shown, by the use of deuterium-labeling that intramolecular acyl migration does not occur in the transformation of cis-monoacetate to the cis-diacetate.

    Ruthenium-catalyzed transfer hydrogenation of 1,3-cyclohexanedione under microwave heating was developed as an efficient and fast method for the preparation of 1,3-cycloalkandiols.

  • 2.
    Norinder, Jakob
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Asymmetric Synthesis and Mechanistic Studies on Copper(I)-Catalyzed Substitution of Allylic Substrates2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with the copper-catalyzed substitution of allylic substrates.

    In the first part of this thesis, the synthesis of a series of metallocenethiolates is described. The thiolates were examined as ligands in the enantioselective copper(I)-catalyzed γ-substitution of allylic acetates.

    The second part describes a study on copper-catalyzed α-substitution of enantiomerically pure secondary allylic esters. It was observed that the degree of chirality transfer is strongly dependent on the reaction temperature. The loss of chiral information is consistent with an equilibration of the allylCu(III) intermediates prior to product formation, which is essential in order to realize a copper-catalyzed dynamic kinetic asymmetric transformation process.

    The third part describes a study on copper-catalyzed stereoselective α-substitution of enantiopure acyclic allylic esters. This method, when combined, with ruthenium and enzyme catalyzed dynamic kinetic resolution of allylic alcohols, provides a straightforward route to pharmaceutically important α-methyl carboxylic acids.

    The fourth part is a mechanistic study on the reaction of perfluoroallyl iodide with organocuprates. Experimental studies as well as theoretical calculations were used to explain the contrasting reactivity of perfluoroallyl iodide vs. allyl iodide in cuprate allylation reactions.

    In the fifth part, the development of a practical and useful method for the preparation of pentasubstituted acylferrocenes is presented.

  • 3.
    Närhi, Katja
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Studies on Palladium-Catalyzed Carbocyclizations of Allene-Substituted Olefins and 1,3-Dienes2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis describes the development and mechanistic studies of carbocyclization reactions of allene-substituted olefins and 1,3-dienes, catalyzed by palladium(0) and palladium(II). These reactions results in the formation of [n,3,0] bicyclic systems (n = 3-5) with high stereoselectivity and in good to excellent yields.

    The first carbocyclization presented is a novel palladium(0)-catalyzed cyclo- isomerization of allene-substituted olefins.

    Secondly an efficient aerobic biomimetic system has been developed for a Pd(II)-catalyzed allylic oxidative carbocyclization of allene-substituted olefins.

    Additionally, during the studies of palladium-catalyzed carbocyclizations of allene-substituted olefins, it was found that in the absence of palladium a mild thermal ene-reaction occurs. In this manner stereodefined, functionalized bicyclic compounds are obtained with good regioselectivity and in high yields.

    The third and fourth carbocyclization developed are a palladium(II)-catalyzed oxidation and a palladium(0)-catalyzed intramolecular telomerization of allene-substituted 1,3-dienes.

    A mechanistic study of the palladium(II)-catalyzed oxidation of allene-substituted 1,3-dienes was made, and reaction intermediates could be isolated. The stereochemistry of the reaction intermediates was assigned, and this made it possible to suggest a mechanism for the reaction. The presented mechanism is a trans carbopalladation of the 1,3-diene, where the allene act as the carbon nucleophile. Due to different stereochemical outcomes of the stoichiometric and catalytic reactions, this mechanism could only explain the stoichiometric reaction. Another mechanism for the catalytic reaction was suggested, which rationalizes both the regio- and stereochemistry of the products.

  • 4.
    Olofsson, Berit
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Aggarwal, Varinder K.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Enantioselective alfa-Arylation of Ketones: Application to the Synthesis of (–)-Epibatidine2006In: Sterochemistry, Bürgenstock, Switzerland, 2006Conference paper (Other (popular science, discussion, etc.))
  • 5.
    Olofsson, Berit
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Aggarwal, Varinder K.
    Bristol University, UK.
    Enantioselective alfa-Arylation of Ketones: Application to the Synthesis of (–)-Epibatidine2006In: Organikerdagarna, Kalmar, Sweden, 2006, p. Le21, P47-Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    The enantioselective introduction of electrophiles alfa to carbonyl compounds occupies a central position in asymmetric synthesis. Although asymmetric alkylations have been well developed, high enantioselectivity in α-arylation of ketones has only been achieved in a limited number of cases.

    We have developed a direct arylation reaction of cyclohexanones, employing diaryl iodonium(III) salts as electrophiles. The reaction was made enantioselective by the use of a chiral base, resulting in 2,4-substituted cyclohexanones in high yields and with high enantiomeric excesses and diastereoselectivities.

    This methodology was applied in a short, enantioselective synthesis of (–)-Epibatidine, an alkaloid recently isolated from the Ecuadorian poison frog Epipedobates tricolor. The synthesis was accomplished in 6 steps and 31% overall yield, thus providing the shortest and most efficient asymmetric route to this important compound to date.

  • 6.
    Olofsson, Berit
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Aggarwal, Varinder K.
    Bristol University, UK.
    Synthesis of Novel Heteroaryl Iodonium Salts and Enantioselective a-Arylation of Cyclohexanones2006In: 2nd Int. Conference on Hypervalent Iodine, 2006Conference paper (Other academic)
    Abstract [en]

    We have developed a direct arylation reaction of cyclohexanones employing diaryl iodonium(Ill) salts as electrophiles. The

    reaction was made enantiosilective by the use of a chiral base, resultinginZ,4-disubstituted cyclohexanones in high yields and with high enantiomeric excesses and diastereoselectivities. Novel heteroaryl iodonium salts were subsequently synthesized and employed in the coupling to variously substituted cyclohexanones.

  • 7.
    Sebelius, Sara
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Palladium-Catalyzed Synthesis and Transformation of Organoboranes2006Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This thesis presents the development of new palladium-catalyzed transformations involving synthesis and application of allylborane reagents. In these reactions various palladium sources, including pincer complexes and commonly used catalysts were applied.

    A new transformation for allylation of aldehyde and imine substrates was devised using allyl acetates, diboronate reagents and catalytic amounts of Pd2(dba)3. By employment of commercially available chiral diboronates enantioenriched homoallyl alcohols could be obtained.

    We have also developed a palladium-catalyzed method for synthesis of functionalized allylboronic acids from vinyl cyclopropane, vinyl aziridine, allyl acetate and allyl alcohol substrates using diboronic acid as reagent. In this process a highly selective selenium based pincer-complex was used as catalyst. The resulting allylboronic acid products were converted to potassium trifluoro(allyl)borates or allylboronates.

    The functionalized allylboronic acids generated in the above procedure were employed as reagents in two synthetic transformations. One of these transformations involves a palladium(0)-catalyzed coupling reaction between allylboronic acids and aryl iodides. The reaction was regioselective for the branched allylic product, typically difficult to prepare in the absence of directing groups. We also developed another transformation for allylation of aldehydes with allyl alcohols via allylboronic acid intermediate. This procedure can be performed as a simple one-pot sequence affording homoallyl alcohols with excellent stereo- and regioselectivity.

  • 8.
    Utas, Josefin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Hydrogen Bonded Phenols as Models for Redox-Active Tyrosines in Enzymes2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with the impact of hydrogen bonding on the properties of phenols. The possibility for tyrosine to form hydrogen bonds to other amino acids has been found to be important for its function as an electron transfer mediator in a number of important redox enzymes. This study has focused on modeling the function of tyrosine in Photosystem II, a crucial enzyme in the photosynthetic pathway of green plants.

    Hydrogen bonds between phenol and amines in both inter- and intramolecular systems have been studied with quantum chemical calculations and also in some solid-state structures involving phenol and imidazole.

    Different phenols linked to amines have been synthesized and their possibilities of forming intra- and intermolecular hydrogen bonds have been studied as well as the thermodynamics and kinetics of the generation of phenoxyl radicals via oxidation reactions.

    Since carboxylates may in principle act as hydrogen bond acceptors in a manner similar to imidazole, proton coupled electron transfer has also been studied for a few phenols intramolecularly hydrogen bonded to carboxylates with the aim to elucidate the mechanism for oxidation. Electron transfer in a new linked phenol—ruthenium(II)trisbipyridine complex was studied as well.

    The knowledge is important for the ultimate goal of the project, which is to transform solar energy into a fuel by an artificial mimic of the natural photosynthetic apparatus

  • 9.
    Utas, Josefin E.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Olofsson, Berit
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Åkermark, Björn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Efficient Synthesis of 2-Substituted Imidazoles by Palladium-Catalyzed Cross-Coupling with Benzylzinc Reagents2006In: Synlett: Accounts and Rapid Communications in Synthetic Organic Chemistry, ISSN 0936-5214, E-ISSN 1437-2096, no 12, p. 1965-1967Article in journal (Refereed)
    Abstract [en]

    Substituted benzylzinc reagents have been used in novel cross-coupling reactions with 2-iodo imidazoles to form compounds containing both a phenol and an imidazole moiety. The ­intramolecular hydrogen-bonding properties of these compounds were subsequently studied.

  • 10.
    Wallner, Olov
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Palladium-Catalyzed Synthesis and Transformations of Organometallic Compounds2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is focused on two important fields of palladium catalysis: the development of electrophilic allylic substitution reactions via bis-allylpalladium intermediates; and application of palladium pincer-complexes in the synthesis and transformations of organometallic compounds.

    Palladium-catalyzed electrophilic allylation of aldehyde and imine substrates could be achieved using readily available allyl chlorides and acetates by employing hexamethylditin or bis(pinacolato)diboron reagents. The reaction proceeds under mild and neutral reaction conditions with high regioselectivity, providing the branched homoallylic products. The stereoselectivity of the reaction depends on the steric and electronic effects of the allylic substituents of the substrates. DFT modeling of the electrophilic attack on the bis-allylpalladium intermediate of the reaction revealed the origin of the regio- and stereoselectivity of the reaction.

    Palladium pincer-complexes were employed as catalysts in a variety of reactions such as stannylation, selenylation, allylation, and cross coupling reactions with various electrophiles. Allylic stannylation in the presence of hexamethylditin was achieved by use of an NCN palladium pincer-complex catalyst. In contrast to the reactions catalyzed by traditional palladium catalysts, isolation of functionalized allyl stannanes was possible due to the special features of the pincer-complex catalyst. Extension of the scope of the palladium pincer-complex catalyzed electrophilic allylation reactions was achieved by using potassium trifluoro(allyl)borate instead of allyl stannanes. In addition, asymmetric electrophilic allylation of sulfonimines was achieved by employment of novel BINOL-based palladium pincer-complexes. The enantioselectivity of the pincer-complex catalyst was fine-tuned by employment of substituted analogs of BINOL.

  • 11.
    Östervall, Jennie
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Conformational Dynamics of Carbohydrates Studied by NMR Spectroscopy and Molecular Simulations2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Carbohydrates play important roles in biological processes. Their function is closely related to their conformation. In this thesis, conformational studies of carbohydrates by NMR spectroscopy and molecular dynamics computer simulations are described.

    The first two papers discuss the anomalous solubility of β-cyclodextrin compared to other cyclodextrins. Time correlation functions revealed flexibility in all cyclodextrins. Molecular dynamics computer simulations showed that the glycosidic linkages were rather rigid and the flexibility was suggested to be macrocyclic. From spatial distribution functions β-cyclodextrin was found to have greater ability to order the surrounding water than the other cyclodextrins. Paper III deals with some of the difficulties of conformational studies. In Paper IV, a new method, Additative Potential Maximum Entropy, APME, is applied to a disaccharide. Conformational distribution functions are derived from NOEs, J-couplings and residual dipolar couplings and calculated from computer simulations. All distribution functions were found to be in good agreement. In papers V and VI oligosaccharides from human milk are studied. Residual dipolar coupling, J-couplings and cross relaxation rates were measured by NMR spectroscopy and molecular dynamics computer simulations were carried out. Both oligosaccharides showed high flexibility for the β-D-GlcpNAc-(1→3)-β-D-Galp linkage.

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