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  • 1.
    Akkarasamiyo, Sunisa
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sawadjoon, Supaporn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Orthaber, Andreas
    Samec, Joseph S. M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Tsuji-Trost Reaction of Non-Derivatized Allylic Alcohols2018In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 24, no 14, p. 3488-3498Article in journal (Refereed)
    Abstract [en]

    Palladium-catalyzed allylic substitution of non-derivatized enantioenriched allylic alcohols with a variety of uncharged N-, S-, C- and O-centered nucleophiles using a bidentate BiPhePhos ligand is described. A remarkable effect of the counter ion (X) of the XPd[kappa(2)-BiPhePhos][kappa(3)-C3H5] was observed. When ClPd[kappa(2)-BiPhePhos][eta(3)-C3H5] (complexI) was used as catalyst, non-reproducible results were obtained. Study of the complex by X-ray crystallography, (PNMR)-P-31 spectroscopy, and ESI-MS showed that a decomposition occurred where one of the phosphite ligands was oxidized to the corresponding phosphate, generating ClPd[kappa(1)-BiPhePhosphite-phosphate][eta(3)-C3H5] species (complexII). When the chloride was exchanged to the weaker coordinating OTf- counter ion the more stable Pd[kappa(2)-BiPhePhos][eta(3)-C3H5](+)+[OTf] (-) (complexIII) was formed. ComplexIII performed better and gave higher enantiospecificities in the substitution reactions. ComplexIII was evaluated in Tsuji-Trost reactions of stereogenic non-derivatized allylic alcohols. The desired products were obtained in good to excellent yields (71-98%) and enantiospecificities (73-99%) for both inter- and intramolecular substitution reactions with only water generated as a by-product. The methodology was applied to key steps in total synthesis of (S)-cuspareine and (+)-lentiginosine. A reaction mechanism involving a palladium hydride as a key intermediate in the activation of the hydroxyl group is proposed in the overall transformation.

  • 2.
    Bartholomeyzik, Teresa
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Pendrill, Robert
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lihammar, Richard
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Jiang, Tuo
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kinetics and Mechanism of the Palladium-Catalyzed Oxidative Arylating Carbocyclization of Allenynes2018In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 140, no 1, p. 298-309Article in journal (Refereed)
    Abstract [en]

    Pd-catalyzed C-C bond-forming reactions under oxidative conditions constitute a class of important and widely used synthetic protocols. This Article describes a mechanistic investigation of the arylating carbocyclization of allenynes using boronic acids and focuses on the correlation between reaction conditions and product selectivity. Isotope effects confirm that either allenic or propargylic C-H activation occurs directly after substrate binding. With an excess of H2O, a triene product is selectively formed via allenic C-H activation. The latter C-H activation was found to be turnover-limiting and the reaction zeroth order in reactants as well as the oxidant. A dominant feature is continuous catalyst activation, which was shown to occur even in the absence of substrate. Smaller amounts of H2O lead to mixtures of triene and vinylallene products, where the latter is formed via propargylic C-H activation. The formation of triene occurs only in the presence of ArB(OH)(2). Vinylallene, on the other hand, was shown to be formed by consumption of (ArBO)(3) as a first-order reactant. Conditions with sub-stoichiometric BF3 center dot OEt2 gave selectively the vinylallene product, and the reaction is first order in PhB(OH)(2). Both C-H activation and transmetalation influence the reaction rate. However, with electron-deficient ArB(OH)(2), C-H activation is turnover-limiting. It was difficult to establish the order of transmetalation vs C-H activation with certainty, but the results suggest that BF3 center dot OEt2 promotes an early transmetalation. The catalytically active species were found to be dependent on the reaction conditions, and H2O is a crucial parameter in the control of selectivity.

  • 3. Betterley, Nolan M.
    et al.
    Kerdphon, Sutthichat
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Chaturonrutsamee, Suppisak
    Kongsriprapan, Sopanat
    Surawatanawong, Panida
    Soorukram, Darunee
    Pohmakotr, Manat
    Andersson, Pher G.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Reutrakul, Vichai
    Kuhakarn, Chutima
    Bi(OTf)(3) Enabled C-F Bond Cleavage in HFIP: Electrophilic Aromatic Formylation with Difluoro(phenylsulfanyl)methane2018In: Asian Journal of Organic Chemistry, ISSN 2193-5807, Vol. 7, no 8, p. 1642-1647Article in journal (Refereed)
    Abstract [en]

    Bismuth(III) trifluoromethanesulfonate [Bi(OTf)(3)] mediated mild electrophilic aromatic formylation utilizing difluoro(phenylsulfanyl)methane (PhSCF2H) as a formylating agent in hexafluoro-2-propanol (HFIP) as a recyclable ionizing solvent has been developed. The active formylating species was generated via C-F bond cleavage and was characterized to be a bis(phenylsulfanyl)methyl cation by experimental and computational H-1 and C-13 NMR.

  • 4.
    Binh, Khanh Mai
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mechanisms of Rh-Catalyzed Oxyfluorination and Oxytrifluoromethylation of Diazocarbonyl Compounds with Hypervalent Fluoroiodine2018In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 8, no 5, p. 4483-4492Article in journal (Refereed)
    Abstract [en]

    The reaction mechanisms of rhodium-catalyzed geminal oxyfluorination and oxytrifluoromethylation of diazo-carbonyl compounds with fluoro-benziodoxole and Togni reagents are investigated by means of density functional theory calculations. It is shown that the two reactions follow very similar mechanisms, involving N-2 dissociation to form a Rh-carbene intermediate, alcohol insertion and proton transfer resulting in a stable Rh-enol intermediate, and concerted proton transfer/electrophilic addition of the hypervalent iodine reagent to the enol. Isomerization of the hypervalent iodine takes then place before a ligand coupling affords the final product. The role of the dirhodium catalyst in facilitating the various steps of the reaction is discussed. The presented mechanisms are consistent with available experimental information, and the obtained insights allow for extension to other reactions involving hypervalent iodine reagents.

  • 5.
    Brea, Oriana
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Luna, Alberto
    Diaz, Cristina
    Corral, Ines
    Molecular Modelling of the H-2-Adsorptive Properties of Tetrazolate-Based Metal-Organic Frameworks: From the Cluster Approach to Periodic Simulations2018In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 19, no 11, p. 1349-1357Article in journal (Refereed)
    Abstract [en]

    Hydrogen has been proposed as a long-term non-fossil fuel to be used in a future ideal carbon-neutral energetic economy. However, its low volumetric energy density hinders its storage and transportation. Metal-organic frameworks (MOFs) represent very promising materials for this purpose due to their very extended surface areas. Azolates, in particular tetrazolates, are - together with carboxylate functionalities - very common organic linkers connecting metallic secondary building units in MOFs. This study addresses, from a theoretical perspective, the H-2 adsorptive properties of tetrazolate linkers at the molecular level, following a size-progressive approach. Specifically, we have investigated how the physisorption energies and geometries are affected when changing the environment of the linker by considering the azolates in the gas phase, immersed in a finite cluster, or being part of an infinite extended crystal material. Furthermore, we also study the H-2 adsorptive capacity of these linkers within the cluster model.

  • 6.
    Brea, Oriana
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mó, Otilia
    Yáñez, Manuel
    Merced Montero-Campillo, M.
    Alkorta, Ibon
    Elguero, José
    Are beryllium-containing biphenyl derivatives efficient anion sponges?2018In: Journal of Molecular Modeling, ISSN 1610-2940, E-ISSN 0948-5023, Vol. 24, no 1, article id 16Article in journal (Refereed)
    Abstract [en]

    The structures and stabilities of 2,2'-diBeX-1,1'-biphenyl (X = H, F, Cl, CN) derivatives and their affinities for F-, Cl-, and CN- were theoretically investigated using a B3LYP/6-311 + G(3df, 2p)//B3LYP/6-31 + G(d,p) model. The results obtained show that the 2,2'-diBeX-1,1'-biphenyl derivatives (X = H, F, Cl, CN) exhibit very high F-, Cl-, and CN- affinities, albeit lower than those reported before for their 1,8-diBeX-naphthalene analogs, in spite of the fact that the biphenyl derivatives are more flexible than their naphthalene counterparts. Nevertheless, some of the biphenyl derivatives investigated are predicted to have anion affinities larger than those measured for SbF5, which is considered one of the strongest anion capturers. Therefore, although weaker than their naphthalene analogs, the 2,2'-diBeX-1,1'-biphenyl derivatives can still be considered powerful anion sponges. This study supports the idea that compounds containing -BeX groups in chelating positions behave as anion sponges due to the electron-deficient nature and consequently high intrinsic Lewis acidity of these groups.

  • 7.
    Colas, Kilian
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mendoza, Abraham
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Iterative Synthesis of Pluripotent Thioethers through Controlled Redox Fluctuation of Sulfur2018In: Synlett: Accounts and Rapid Communications in Synthetic Organic Chemistry, ISSN 0936-5214, E-ISSN 1437-2096, Vol. 29, no 10, p. 1329-1333Article in journal (Refereed)
    Abstract [en]

    Target- and diversity-oriented syntheses are based on diverse building blocks, whose preparation requires discrete design and constructive alignment of different chemistries. To enable future automation of the synthesis of small molecules, we have devised a unified strategy that serves the divergent synthesis of unrelated scaffolds such as carbonyls, olefins, organometallics, halides, and boronic esters. It is based on iterations of a nonelectrophilic Pummerer-type C-C coupling enabled by turbo -organomagnesium amides that we have recently reported. The pluripotency of sulfur allows the central building blocks to be obtained by regulating C-C bond formation through control of its redox state.

  • 8.
    Cortés González, Miguel A.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Nordeman, Patrik
    Bermejo Gómez, Antonio
    Stockholm University, Faculty of Science, Department of Organic Chemistry. AstraZeneca PET Centre at Karolinska Institutet, Sweden.
    Meyer, Denise N.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Antoni, Gunnar
    Schou, Magnus
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    [F-18]fluoro-benziodoxole: a no-carrier-added electrophilic fluorinating reagent. Rapid, simple radiosynthesis, purification and application for fluorine-18 labelling2018In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 54, no 34, p. 4286-4289Article in journal (Refereed)
    Abstract [en]

    Operationally simple radiosynthesis and purification of [F-18]fluoro-benziodoxole was developed starting from a cyclotron produced [F-18]F- precursor, [F-18]TBAF, and tosyl-benziodoxole. The synthetic utility of [F-18]fluoro-benziodoxole was demonstrated by electrophilic fluorocyclization of o-styrilamides proceeding with high RCC (typically 50-90%) and high molar activity (up to 396 GBq mol(-1)).

  • 9. Daikoku, S.
    et al.
    Pendrill, Robert
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kanie, Y.
    Ito, Y.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kanie, O.
    Synthesis and structural investigation of a series of mannose-containing oligosaccharides using mass spectrometry2018In: Organic and biomolecular chemistry, ISSN 1477-0520, E-ISSN 1477-0539, Vol. 16, no 2, p. 228-238Article in journal (Refereed)
    Abstract [en]

    A series of compounds associated with naturally occurring and biologically relevant glycans consisting of alpha-mannosides were prepared and analyzed using collision-induced dissociation (CID), energy-resolved mass spectrometry (ERMS), and H-1 nuclear magnetic resonance spectroscopy. The CID experiments of sodiated species of disaccharides and ERMS experiments revealed that the order of stability of mannosyl linkages was as follows: 6-linked > 4-linked >= 2-linked > 3-linked mannosyl residues. Analysis of linear trisaccharides revealed that the order observed in disaccharides could be applied to higher glycans. A branched trisaccharide showed a distinct dissociation pattern with two constituting disaccharide ions. The estimation of the content of this ion mixture was possible using the disaccharide spectra. The hydrolysis of mannose linkages at 3- and 6-positions in the branched trisaccharide revealed that the 3-linkage was cleaved twice as fast as the 6-linkage. It was observed that the solution-phase hydrolysis and gas-phase dissociation have similar energetics.

  • 10. Dorau, Robin
    et al.
    Görbe, Tamás
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Svedendahl Humble, Maria
    Improved Enantioselectivity of Subtilisin Carlsberg Towards Secondary Alcohols by Protein Engineering2018In: ChemBioChem (Print), ISSN 1439-4227, E-ISSN 1439-7633, Vol. 19, no 4, p. 338-346Article in journal (Refereed)
    Abstract [en]

    Generally, the catalytic activity of subtilisin Carlsberg (SC) for transacylation reactions with secondary alcohols in organic solvent is low. Enzyme immobilization and protein engineering was performed to improve the enantioselectivity of SC towards secondary alcohols. Possible amino-acid residues for mutagenesis were found by combining available literature data with molecular modeling. SC variants were created by site-directed mutagenesis and were evaluated for a model transacylation reaction containing 1-phenylethanol in THF. Variants showing high E values (>100) were found. However, the conversions were still low. A second mutation was made, and both the E values and conversions were increased. Relative to that shown by the wild type, the most successful variant, G165L/M221F, showed increased conversion (up to 36 %), enantioselectivity (E values up to 400), substrate scope, and stability in THF.

  • 11.
    González Miera, Greco
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Martínez-Castro, Elisa
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Martín-Matute, Belén
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Acceptorless Alcohol Dehydrogenation: OH vs NH Effect in Bifunctional NHC–Ir(III) Complexes2018In: Organometallics, ISSN 0276-7333, E-ISSN 1520-6041, Vol. 37, no 5, p. 636-644Article in journal (Refereed)
    Abstract [en]

    Bifunctional complexes bearing N-heterocyclic carbene (NHC) ligands functionalized with hydroxy or amine groups were synthesized to measure the beneficial effect of different modes of metal–ligand cooperation in the acceptorless dehydrogenation of alcohols. In comparison to complexes with an amine moiety, hydroxy-functionalized iridium catalysts showed superior activity. In contrast to alcohols, 1,4-diols underwent cyclization to give the corresponding tetrahydrofurans without involving dehydrogenation processes. Mechanistic investigations to rationalize the “OH effect” in these types of complexes have been undertaken.

  • 12.
    Gudmundsson, Arnar
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Gustafson, Karl P. J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Yang, Bin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Efficient Formation of 2,3-Dihydrofurans via Iron-Catalyzed Cycloisomerization of alpha-Allenols2018In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 8, no 1, p. 12-16Article in journal (Refereed)
    Abstract [en]

    Herein, we report a highly efficient iron-catalyzed intramolecular nucleophilic cyclization of alpha-allenols to furnish substituted 2,3-dihydrofurans under mild reaction conditions. A highly diastereoselective variant of the reaction was developed as well, giving diastereomeric ratios of up to 98:2. The combination of the iron-catalyzed cycloisomerization with enzymatic resolution afforded the 2,3-dihydrofuran in high ee. A detailed DFT study provides insight into the reaction mechanism and gives a rationalization for the high chemo-and diastereoselectivity.

  • 13.
    Görbe, Tamás
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lihammar, Richard
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Heterogeneous Acid-Catalyzed Racemization of Tertiary Alcohols2018In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 24, no 1, p. 77-80Article in journal (Refereed)
    Abstract [en]

    Tertiary alcohols are important structural motifs in natural products and building blocks in organic synthesis but only few methods are known for their enantioselective preparation. Chiral resolution is one of these approaches that leaves one enantiomer (50% of the material) unaffected. An attractive method to increase the efficiency of those resolutions is to racemize the unaffected enantiomer. In the present work, we have developed a practical racemization protocol for tertiary alcohols. Five different acidic resin materials were tested. The Dowex 50WX8 was the resin of choice since it was capable of racemizing tertiary alcohols without any byproduct formation. Suitable solvents and a biphasic system were investigated, and the optimized system was capable of racemizing differently substituted tertiary alcohols.

  • 14.
    Heshmat, Mojgan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Structurally Flexible Oxocarbenium/Borohydride Ion Pair: Dynamics of Hydride Transfer on the Background of Conformational Roaming2018In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 122, no 23, p. 5098-5106Article in journal (Refereed)
    Abstract [en]

    We apply Born-Oppenheimer molecular dynamics to the practically significant [dioxane-H(+)-acetone]-[(C6F5)(3)B-H(-)] and [Et2O-H(+)-OCPr2][(C6F5)(3)B-H(-)] ion pair intermediates. Dynamics of hydride transfer in cation/anion ion pair takes place on the background of large amplitude configurational changes. Geometry of oxocarbenium/borohydride ion pairs is flexible, meaning that we uncover significant actual structural disorder at a finite temperature. Therefore, although the starting structure can be fairly close to the configurational area of the hydride transfer transition state (TS) and despite a low potential energy barrier (ca. 1.5 kcal/mol, according to the literature), already at T approximate to 325 K the system can remain ignorant of the TS region and move round and about (roam) in the configurational space for a period of time in the range between 10 and 100 ps. This indicates structural flexibility of oxocarbenium/borohydride ion pair on apparently a flat potential energy landscape of cation/anion interaction, and this has not been taken into consideration by the free energy estimations in static considerations made thus far. The difference between the dynamics-based representation of the system versus the static representation amounts to the difference between quasi-bimolecular versus unimolecular descriptions of the hydride transfer step.

  • 15.
    Heshmat, Mojgan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Surprisingly Flexible Oxonium/Borohydride Ion Pair Configurations2018In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 122, no 15, p. 3713-3727Article in journal (Refereed)
    Abstract [en]

    We investigate the geometry of oxonium/borohydride ion pairs [ether-H(+) ether] [LA-H(-)] with dioxane, THF, and Et2O as ethers and B(C6F5)(3) as the Lewis acid (LA). The question is about possible location of the disolvated proton [ether -H(+) -ether], with respect to the hydride of the structurally complex [LA -H(-)] anion. Using Born Oppenheimer molecular dynamics and a comparison of the potential and free energies of the optimized configurations, we show that herein considered ion pairs are much more flexible geometrically than previously thought. Conformers with different locations of cations with respect to anions are governed by a flat energy -landscape. We found a novel configuration in which oxonium is below [LA-11((-))], with respect to the direction of borane -> hydride vector, and the proton -hydride distance is ca. 6 A. With calculations of the vibrational spectra of [ether-H(+)-ether][(C6F5)(3)B-H(-)] for dioxane, THF, and Et2O as ethers, we investigate the manifestation of SSLB-type (short, strong, low -barrier) hydrogen bonding in the OHO motif of an oxonium cation.

  • 16. Ibrahem, Ismail
    et al.
    Iqbal, Muhammad Naeem
    Stockholm University, Faculty of Science, Department of Organic Chemistry. Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Verho, Oscar
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Eivazihollagh, Alireza
    Olsén, Peter
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Edlund, Håkan
    Tai, Cheuk-Wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Norgren, Magnus
    Johnston, Eric V.
    Copper Nanoparticles on Controlled Pore Glass and TEMPO for the Aerobic Oxidation of Alcohols2018In: ChemNanoMat, ISSN 2199-692X, Vol. 4, no 1, p. 71-75Article in journal (Refereed)
    Abstract [en]

    Herein, we report on the facile synthesis of a heterogeneous copper nanocatalyst and its combination with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) for the aerobic oxidation of alcohols to their corresponding carbonyl compounds. This low cost copper nanocatalyst was found to exhibit excellent recyclability, making it a highly attractive catalytic system from an economical and environmental point of view. Extensive characterization of the catalyst by a number of techniques revealed that it was comprised of well-dispersed Cu(I/II) nanoparticles with an average size of around 6nm.

  • 17.
    Jiang, Yan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Deiana, Luca
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Alimohammadzadeh, Rana
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Liu, Leifeng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Sun, Junliang
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Cordova, Armando
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Highly Diastereo- and Enantioselective Cascade Synthesis of Bicyclic Lactams in One-Pot2018In: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, no 9, p. 1158-1164Article in journal (Refereed)
    Abstract [en]

    A versatile and highly stereoselective synthetic route to functionalized bi- and tricyclic lactams (up to > 20:1 dr and 99% ee) in one pot from simple starting materials (allylic alcohols, enals, diamines and amino alcohols) using cascade transformations promoted by chiral amine/BrOnsted or metal/chiral amine/BrOnsted relay catalysis is disclosed. Here molecular oxygen is employed as the terminal oxidant for the latter relay catalysis approach.

  • 18. Jo, Sunhwan
    et al.
    Myatt, Daniel
    Qi, Yifei
    Doutch, James
    Clifton, Luke A.
    Im, Wonpil
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Multiple Conformational States Contribute to the 3D Structure of a Glucan Decasaccharide: A Combined SAXS and MD Simulation Study2018In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 122, no 3, p. 1169-1175Article in journal (Refereed)
    Abstract [en]

    The inherent flexibility of carbohydrates is dependent on stereochemical arrangements, and characterization of their influence and importance will give insight into the three-dimensional structure and dynamics. In this study, a beta-(1 -> 4)/beta-(1 -> 3)-linked glucosyl decasaccharide is experimentally investigated by synchrotron small-angle X-ray scattering from which its radius of gyration (R-g) is obtained. Molecular dynamics (MD) simulations of the decasaccharide show four populated states at each glycosidic linkage, namely, syn- and anti-conformations. The calculated R-g values from the MD simulation reveal that in addition to syn-conformers the presence of anti-psi conformational states is required to reproduce experimental scattering data, unveiling inherent glycosidic linkage flexibility. The CHARMM36 force field for carbohydrates thus describes the conformational flexibility of the decasaccharide very well and captures the conceptual importance that anti-conformers are to be anticipated at glycosidic linkages of carbohydrates.

  • 19.
    Kazemi, Masoud
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry. Uppsala University, Sweden.
    Socan, Jaka
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Åqvist, Johan
    Mechanistic alternatives for peptide bond formation on the ribosome2018In: Nucleic Acids Research, ISSN 0305-1048, E-ISSN 1362-4962, Vol. 46, no 11, p. 5345-5354Article in journal (Refereed)
    Abstract [en]

    The peptidyl transfer reaction on the large ribosomal subunit depends on the protonation state of the amine nucleophile and exhibits a large kinetic solvent isotope effect (KSIE similar to 8). In contrast, the related peptidyl-tRNA hydrolysis reaction involved in termination shows a KSIE of similar to 4 and a pH-rate profile indicative of base catalysis. It is, however, unclear why these reactions should proceed with different mechanisms, as the experimental data suggests. One explanation is that two competing mechanisms may be operational in the peptidyl transferase center (PTC). Herein, we explored this possibility by re-examining the previously proposed proton shuttle mechanism and testing the feasibility of general base catalysis also for peptide bond formation. We employed a large cluster model of the active site and different reaction mechanisms were evaluated by density functional theory calculations. In these calculations, the proton shuttle and general base mechanisms both yield activation energies comparable to the experimental values. However, only the proton shuttle mechanism is found to be consistent with the experimentally observed pH-rate profile and the KSIE. This suggests that the PTC promotes the proton shuttle mechanism for peptide bond formation, while prohibiting general base catalysis, although the detailed mechanism by which general base catalysis is excluded remains unclear.

  • 20. Kiss, Anita
    et al.
    Herman, Bianka Edina
    Görbe, Tamás
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mernyak, Erzsebet
    Molnar, Barnabas
    Wolfling, Janos
    Szecsi, Mihaly
    Schneider, Gyula
    Synthesis of novel 17-triazolyl-androst-5-en-3-ol epimers via Cu(I)-catalyzed azide-alkyne cycloaddition and their inhibitory effect on 17 alpha-hydroxylase/ C-17,C-20-lyase2018In: Steroids, ISSN 0039-128X, E-ISSN 1878-5867, Vol. 135, p. 79-91Article in journal (Refereed)
    Abstract [en]

    The regioselective Cu(I)-catalyzed 1,3-dipolar cycloaddition of 17 alpha- and 17 beta-azidoandrost-5-en-3 beta-ol epimers (3b and 5b) with different terminal alkynes afforded novel 1,4-substituted triazolyl derivatives (8a-k and 9a-k). For the preparation of 5'-iodo-l',2',3'-triazoles (8m-n and 9m-n), an improved method was developed, directly from steroidal azides and terminal alkynes, in reaction mediated by Cul and IC1 as iodinating agents. Acetolysis and subsequent hydrolysis of 8n and 9n yielded 5'-hydroxy-l',2',3'-triazoles 8o and 9o. The inhibitory effect of 8a-o, 9a-o, 3, and 5 on rat testicular C-17,C-20-lyase was investigated by means of an in vitro radioincubation technique. The results revealed that the C-17 epimers of steroidal triazoles influence the C-17,C-20-lyase effect. Inhibitors were found only in the 17 alpha-triazolyl series (8a-o), whereas in the C-17 azide pair the 17 beta compound (5b) was more potent.

  • 21.
    Krajangsri, Suppachai
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Yang, Jianping
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Massaro, Luca
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Andersson, Pher
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Iridium-Catalysed Enantioselective Hydrogenation of Enamides2018Manuscript (preprint) (Other academic)
    Abstract [en]

    A variety of oxazolidinone-enamides were prepared and evaluated in this reaction. High yields, (up to 99%) and excellent ee, (up to 99%) were obtained.

  • 22.
    Kumaniaev, Ivan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Samec, Joseph S. M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Valorization of Quercus suber Bark toward Hydrocarbon Bio-Oil and 4-Ethylguaiacol2018In: ACS sustainable chemistry and engineering, ISSN 2168-0485, Vol. 6, no 5, p. 5737-5742Article in journal (Refereed)
    Abstract [en]

    A reductive fractionation process for the valorization of Quercus suber bark toward hydrocarbons in gasoline and diesel ranges and optionally 4-ethylguaiacol has been developed. The procedure involves three steps: (1) tandem hydrogen-free Pd/C-catalyzed transfer hydrogenolysis of lignin where the carbohydrates serve as an inherent hydrogen donor under slightly alkaline conditions to also facilitate the depolymerization of suberin, (2) optional distillation, to isolate the 4-ethylguaiacol, (3) hydrodeoxygenation of the mixture from the first step by a Pt-MoO3/TiO2 catalyst generated hydrocarbons in gasoline and diesel ranges. The yield of 4-ethylguaiacol (90% purity) is 2.6% of dry bark weight (12% of acid insoluble lignin), and yield of hydrocarbon bio-oil is 42% of dry bark weight. This corresponds to a theoretical maximum yield of 77% for lignin and suberin. The carbon yield of the obtained bio-oil is thereby 64% from the total initial bark.

  • 23.
    Lati, Monireh Pourghasemi
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry. University of Zanjan, Iran.
    Naeem, Muhammad Iqbal
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Alinia-Asli, Mokhtar
    Shirini, Farhad
    Rezvani, Mohammad Ali
    Åkermark, Björn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Johnston, Eric
    Verho, Oscar
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Palladium Nanoparticles Immobilized on an Aminopropyl-functionalized Silica-Magnetite Composite as a Recyclable Catalyst for Suzuki-Miyaura Reactions2018In: Chemistryselect, ISSN 2365-6549, Vol. 3, no 27, p. 7970-7975Article in journal (Refereed)
    Abstract [en]

    Herein, we describe the straightforward synthesis and thorough characterization of a magnetically-separable heterogeneous catalyst comprised of 1-3nm-sized Pd nanoparticles immobilized on a mesoporous silica-magnetite composite (Pd-0-AmP-SMC). Catalytic evaluations were conducted using Suzuki-Miyaura cross-couplings as the model reactions, for which this Pd nanocatalyst exhibited high performance in an environmentally-friendly solvent mixture. Additionally, this Pd nanocatalyst could be re-used up to five cycles without any observable loss of activity, and separation of the catalyst could be conveniently done by a magnet.

  • 24.
    Margarita, Cristiana
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Rabten, Wangchuk
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Andersson, Pher G.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Transition-Metal-Catalyzed Regioselective Asymmetric Mono-Hydrogenation of Dienes and Polyenes2018In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 24, no 32, p. 8022-8028Article in journal (Refereed)
    Abstract [en]

    Organic compounds containing multiple C=C bonds are attractive substrates for catalytic asymmetric hydrogenation. The full saturation of prochiral double bonds, controlling the creation of two or more stereocenters in one step, is obviously a remarkable goal. However, another fascinating and useful option is to selectively introduce a new defined stereogenic center while leaving other double bonds untouched. Thus, the retained functionalities can be further exploited in synthesis. Examples of regio- and enantioselective mono-hydrogenations of polyolefins are highlighted in this Concept article, and are divided according to the nature of the reduced double bond and the transition-metal catalyst used. Alkenes bearing coordinating functional groups are often preferentially hydrogenated by Rh- and Ru-complexes, while the more recently developed Ir-based catalysts promote the selective saturation on alkyl-substituted olefins. Relevant applications of this effective methodology in the synthesis of natural products are included to demonstrate its value in organic synthesis.

  • 25. Martínez-Gómez, Estrella
    et al.
    Ståhle, Jonas
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Gil-Ramírez, Yolanda
    Zúñiga-Ripa, Amaia
    Zaccheus, Mona
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Moriyón, Ignacio
    Iriarte, Maite
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Conde-Álvarez, Raquel
    Genomic Insertion of a Heterologous Acetyltransferase Generates a New Lipopolysaccharide Antigenic Structure in Brucella abortus and Brucella melitensis2018In: Frontiers in Microbiology, ISSN 1664-302X, E-ISSN 1664-302X, Vol. 9, article id 1092Article in journal (Refereed)
    Abstract [en]

    Brucellosis is a bacterial zoonosis of worldwide distribution caused by bacteria of the genus Brucella. In Brucella abortus and Brucella melitensis, the major species infecting domestic ruminants, the smooth lipopolysaccharide (S-LPS) is a virulence factor. This S-LPS carries a N-formyl-perosamine homopolymer O-polysaccharide that is the major antigen in serodiagnostic tests and is required for virulence. We report that the Brucella O-PS can be structurally and antigenically modified using wbdR, the acetyl-transferase gene involved in N-acetyl-perosamine synthesis in Escherichia coli O157:H7. Brucella constructs carrying plasmidic wbdR expressed a modified O-polysaccharide but were unstable, a problem circumvented by inserting wbdR into a neutral site of chromosome II. As compared to wild-type bacteria, both kinds of wbdR constructs expressed shorter O-polysaccharides and NMR analyses showed that they contained both N-formyl and N-acetyl-perosamine. Moreover, deletion of the Brucella formyltransferase gene wbkC in wbdR constructs generated bacteria producing only N-acetyl-perosamine homopolymers, proving that wbdR can replace for wbkC. Absorption experiments with immune sera revealed that the wbdR constructs triggered antibodies to new immunogenic epitope(s) and the use of monoclonal antibodies proved that B. abortus and B. melitensis wbdR constructs respectively lacked the A or M epitopes, and the absence of the C epitope in both backgrounds. The wbdR constructs showed resistance to polycations similar to that of the wild-type strains but displayed increased sensitivity to normal serum similar to that of a per R mutant. In mice, the wbdR constructs produced chronic infections and triggered antibody responses that can be differentiated from those evoked by the wild-type strain in S-LPS ELISAs. These results open the possibilities of developing brucellosis vaccines that are both antigenically tagged and lack the diagnostic epitopes of virulent field strains, thereby solving the diagnostic interference created by current vaccines against Brucella.

  • 26.
    Olsén, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Morvan, Jennifer
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sawadjoon, Supaporn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Shatskiy, Andrey
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Johnston, Eric V.
    Åkermark, Björn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Cyclic allylic carbonates as a renewable platform for protecting chemistry in water2018In: Green Chemistry, ISSN 1463-9262, E-ISSN 1463-9270, Vol. 20, no 14, p. 3186-3190Article in journal (Refereed)
    Abstract [en]

    The present work explores different cyclic allylic carbonates as a potential class of allylcarbamate precursors. The 5-membered carbonate formed a carbamate with very good thermal and pH stability, which could be cleanly deprotected in aqueous solution, in just 30 min with 2 mol% Pd(OAc)(2) as catalyst. The polar nature of the installed motif made it possible to deprotect highly unpolar substrates in water as solvent.

  • 27.
    Olsén, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Oschmann, Michael
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Johnston, Eric V.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Åkermark, Björn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis of highly functional carbamates through ring-opening of cyclic carbonates with unprotected alpha-amino acids in water2018In: Green Chemistry, ISSN 1463-9262, E-ISSN 1463-9270, Vol. 20, no 2, p. 469-475Article in journal (Refereed)
    Abstract [en]

    The present work shows that it is possible to ring-open cyclic carbonates with unprotected amino acids in water. Fine tuning of the reaction parameters made it possible to suppress the degree of hydrolysis in relation to aminolysis. This enabled the synthesis of functionally dense carbamates containing alkenes, carboxylic acids, alcohols and thiols after short reaction times at room temperature. When Glycine was used as the nucleophile in the ring-opening with four different five membered cyclic carbonates, containing a plethora of functional groups, the corresponding carbamates could be obtained in excellent yields (> 90%) without the need for any further purification. Furthermore, the orthogonality of the transformation was explored through ring-opening of divinylenecarbonate with unprotected amino acids equipped with nucleophilic side chains, such as serine and cysteine. In these cases the reaction selectively produced the desired carbamate, in 70 and 50% yield respectively. The synthetic design provides an inexpensive and scalable protocol towards highly functionalized building blocks that are envisioned to find applications in both the small and macromolecular arena.

  • 28. Orebom, Alexander
    et al.
    Verendel, J. Johan
    Samec, Joseph S. M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry. RenFuel AB, Sweden.
    High Yields of Bio Oils from Hydrothermal Processing of Thin Black Liquor without the Use of Catalysts or Capping Agents2018In: ACS omega, ISSN 2470-1343, Vol. 3, no 6, p. 6757-6763Article in journal (Refereed)
    Abstract [en]

    Black liquor (BL) from the kraft pulping process has been treated at elevated temperatures (380 degrees C) in a batch reactor to give high yields of a bio oil comprising monomeric phenolic compounds that were soluble in organic solvents and mineral oil and a water fraction with inorganic salts. The metal content in the product was < 20 ppm after a simple extraction step. A correlation between concentration, temperature, and reaction time with respect to yield of desired product was found. At optimal reaction conditions (treating BL with 16 wt % dry substance at 380 degrees C for 20 min), the yield of extractable organics was around 80% of the original lignin with less than 7% of char. The product was analyzed by gel permeable chromatography, mass spectroscopy, nuclear magnetic resonance, elemental analysis, and inductively coupled plasma. It was found that a large fraction composed of mainly cresols, xylenols, and mesitols. This process provides a pathway to convert a major waste stream from a pulp mill into a refinery feed for fuel or chemical production, whereas at the same time the inorganic chemicals are recovered and can be returned back to the pulp mill.

  • 29.
    Pathipati, Stalin R.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    van der Werf, Angela
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Selander, Nicklas
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Diastereoselective Synthesis of Polycyclic Indolizines with 2-(2-Enynyl)pyridines and Enamines2018In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 20, no 12, p. 3691-3694Article in journal (Refereed)
    Abstract [en]

    A diastereoselective metal-catalyzed reaction of 2-(2-enynyl)pyridines and cyclic enamines is reported. The method provides access to a variety of substituted indolizine derivatives by variation of the enyne component and the reaction conditions. Performing the reaction using a preformed enamine led to the formation of polycyclic indolizines. With in situ generated enamines, ketone-containing indolizine derivatives were obtained. An asymmetric reaction of 2-(2-enynyl)pyridines and enamines generated from an aldehyde and a catalytic amount of amine is presented.

  • 30.
    Planas, Ferran
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sheng, Xiang
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    McLeish, Michael J.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    A Theoretical Study of the Benzoylformate Decarboxylase Reaction Mechanism2018In: Frontiers in Chemistry, E-ISSN 2296-2646, Vol. 6, article id 205Article in journal (Refereed)
    Abstract [en]

    Density functional theory calculations are used to investigate the detailed reaction mechanism of benzoylformate decarboxylase, a thiamin diphosphate (ThDP)-dependent enzyme that catalyzes the nonoxidative decarboxylation of benzoylformate yielding benzaldehyde and carbon dioxide. A large model of the active site is constructed on the basis of the X-ray structure, and it is used to characterize the involved intermediates and transition states and evaluate their energies. There is generally good agreement between the calculations and available experimental data. The roles of the various active site residues are discussed and the results are compared to mutagenesis experiments. Importantly, the calculations identify off-cycle intermediate species of the ThDP cofactor that can have implications on the kinetics of the reaction.

  • 31. Pope, Giovanna M.
    et al.
    Hung, Ivan
    Gan, Zhehong
    Mobarak, Hani
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Harper, James K.
    Exploiting C-13/N-14 solid-state NMR distance measurements to assign dihedral angles and locate neighboring molecules2018In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 54, no 49, p. 6376-6379Article in journal (Refereed)
    Abstract [en]

    The RESPDOR NMR method rapidly provides multiple C-13/N-14 distance measurements in natural abundance solids. In this study, C-13/N-14 RESPDOR information is shown, for the first time, to provide accurate molecular conformation and to locate non-bonded neighboring molecules.

  • 32.
    Posevins, Daniels
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Qiu, Youai
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Highly Diastereoselective Palladium-Catalyzed Oxidative Carbocyclization of Enallenes Assisted by a Weakly Coordinating Hydroxyl Group2018In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 140, no 9, p. 3210-3214Article in journal (Refereed)
    Abstract [en]

    A highly diastereoselective palladium-catalyzed oxidative carbocyclization-borylation of enallenes assisted by a weakly coordinating hydroxyl group was developed. The reaction afforded functionalized cyclo-hexenol derivatives, in which the 1,3-relative stereo chemistry is controlled (d.r. > 50:1). Other weakly coordinating oxygen-containing groups (ketone, alkoxide, acetate) also assisted the carbocyclization toward cyclo-hexenes. The reaction proceeds via a ligand exchange on Pd of the weakly coordinating group with a distant olefin group. The high diastereoselectivity of the hydroxyl directed reaction could be rationalized by a face-selective coordination of the distant olefin. It was demonstrated that the primary coordination of the close-by oxygen containing functionality was necessary for the reaction to occur and removal of this functionality shut down the reaction.

  • 33.
    Qiu, Youai
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mendoza, Abraham
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Posevins, Daniels
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kalek, Marcin
    Bäckvall, Jan E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mechanistic Insight into Enantioselective Palladium-Catalyzed Oxidative Carbocyclization-Borylation of Enallenes2018In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 24, no 10, p. 2433-2439Article in journal (Refereed)
    Abstract [en]

    The asymmetric palladium-catalyzed oxidative carbocyclization-borylation of enallenes, employing a chiral phosphoric acid as co-catalyst, constitutes an efficient and convenient entry into functionalized building blocks with cyclopentene scaffolds in high enantiopurity. Up till now there has been a lack of knowledge concerning the origin of enantioselectivity of this reaction as well as the absolute configuration of the product. Herein, we report the crystal structure of one of the compounds generated via this carbocyclization, providing the link between the configuration of the products and the configuration of the chiral phosphoric acid used in the reaction. Furthermore, the origin of the enantioselectivity is thoroughly investigated with density functional theory (DFT) calculations. By careful examination of different possible coordination modes, it is shown that the chiral phosphoric acid and the corresponding phosphate anion serve as ligands for palladium during the key stereoselectivity-determining cyclization step. In addition, we examine reactions wherein an extra chiral reagent, a p-benzoquinone containing a chiral sulfoxide, is used. The combined experimental and theoretical studies provide insight into the details of complexation of palladium with various species present in the reaction mixture, furnishing a general understanding of the factors governing the stereoselectivity of this and related catalytic reactions.

  • 34.
    Reitti, Marcus
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Gurubrahamam, Ramani
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Walther, Melanie
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lindstedt, Erik
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Olofsson, Berit
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis of Phenols and Aryl Silyl Ethers via Arylation of Complementary Hydroxide Surrogates2018In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 20, no 7, p. 1785-1788Article in journal (Refereed)
    Abstract [en]

    Two transition-metal-free methods to access substituted phenols via the arylation of silanols or hydrogen peroxide with diaryliodonium salts are presented. The complementary reactivity of the two nucleophiles allows synthesis of a broad range of phenols without competing aryne formation, as illustrated by the synthesis of the anesthetic Propofol. Furthermore, silyl-protected phenols can easily be obtained, which are suitable for further transformations.

    The full text will be freely available from 2019-03-14 01:00
  • 35.
    Rukkijakan, Thanya
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Akkarasamiyo, Sunisa
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sawadjoon, Supaporn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Samec, Joseph S. M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Pd-Catalyzed Substitution of the OH Group of Nonderivatized Allylic Alcohols by Phenols2018In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 83, no 7, p. 4099-4104Article in journal (Refereed)
    Abstract [en]

    Nonactivated phenols have been employed as nucleophiles in the allylation of nonderivatized allylic alcohols to generate allylated phenolic ethers with water as the only byproduct. A Pd[BiPhePhos] catalyst was found to be reactive to give the O-allylated phenols in good to excellent yields in the presence of molecular sieves. The reactions are chemo-selective in which the kinetically favored O-allylated products are formed exclusively over the thermodynamically favored C-allylated products.

  • 36. Santoro, Stefano
    et al.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mechanism and selectivity of rhodium-catalyzed CH bond arylation of indoles2018In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 118, no 9, article id e25526Article in journal (Refereed)
    Abstract [en]

    Density functional theory calculations are used to study the reaction mechanism and origins of C2-selectivity in a rhodium-catalyzed arylation of indole. It is shown that the reaction is catalyzed by an anionic Rh(III)-intermediate that activates the substrate through a concerted-metalation deprotonation. Dissociation of pivalic acid and subsequent reductive elimination generate the arylated indole product. Oxidative addition of the aryl iodide and a subsequent ligand exchange regenerates the active catalytic species. The origin of the regioselectivity is found to be the more favorable interaction between the 2-indolyl fragment and the metal center compared to the 3-indolyl fragment. Moreover, the better interaction of the pivalate ligands with the substrate in the transition state for the activation of C2H compared to the transition state for the C3H activation further favors the C2-selectivity.

  • 37.
    Sanz-Marco, Amparo
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Martinez-Erro, Samuel
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Martín-Matute, Belén
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Selective Synthesis of Unsymmetrical Aliphatic Acyloins through Oxidation of Iridium Enolates2018In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 24, no 45, p. 11564-11567Article in journal (Refereed)
    Abstract [en]

    The first method to access unsymmetrical aliphatic acyloins is presented. The method relies on a fast 1,3-hydride shift mediated by an Ir-III complex in allylic alcohols followed by oxidation with TEMPO+. The direct conversion of allylic alcohols into acyloins is achieved in a one-pot procedure. Further functionalization of the C alpha' of the alpha-amino-oxylated ketone products gives access to highly functionalized unsymmetrical aliphatic ketones, which further highlights the utility of this transformation.

  • 38.
    Sheng, Xiang
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Patskovsky, Yury
    Vladimirova, Anna
    Bonanno, Jeffrey B.
    Almo, Steven C.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Raushel, Frank M.
    Mechanism and Structure of gamma-Resorcylate Decarboxylase2018In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 57, no 22, p. 3167-3175Article in journal (Refereed)
    Abstract [en]

    gamma-Resorcylate decarboxylase (gamma-RSD) has evolved to catalyze the reversible decarboxylation of 2,6-dihydroxybenzoate to resorcinol in a nonoxidative fashion. This enzyme is of significant interest because of its potential for the production of gamma-resorcylate and other benzoic acid derivatives under environmentally sustainable conditions. Kinetic constants for the decarboxylation of 2,6-dihydroxybenzoate catalyzed by gamma-RSD from Polaromonas sp. JS666 are reported, and the enzyme is shown to be active with 2,3-dihydroxybenzoate, 2,4,6-trihydroxybenzoate, and 2,6-dihydroxy-4-methylbenzoate. The three-dimensional structure of gamma-RSD with the inhibitor 2-nitroresorcinol (2-NR) bound in the active site is reported. 2-NR is directly ligated to a Mn2+ bound in the active site, and the nitro substituent of the inhibitor is tilted significantly from the plane of the phenyl ring. The inhibitor exhibits a binding mode different from that of the substrate bound in the previously determined structure of gamma-RSD from Rhizobtum sp. MTP-10005. On the basis of the crystal structure of the enzyme from Polaromonas sp. JS666, complementary density functional calculations were performed to investigate the reaction mechanism. In the proposed reaction mechanism, gamma-RSD binds 2,6-dihydroxybenzoate by direct coordination of the active site manganese ion to the carboxylate anion of the substrate and one of the adjacent phenolic oxygens. The enzyme subsequently catalyzes the transfer of a proton to Cl of y-resorcylate prior to the actual decarboxylation step. The reaction mechanism proposed previously, based on the structure of gamma-RSD from Rhizobtum sp. MTP-10005, is shown to be associated with high energies and thus less likely to be correct.

  • 39.
    Siegbahn, Per E. M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    A Major Structural Change of the Homocitrate Ligand of Probable Importance for the Nitrogenase Mechanism2018In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 57, no 3, p. 1090-1095Article in journal (Refereed)
    Abstract [en]

    Mo-containing nitrogenase is the main enzyme that is able to take N-2 from the air and form ammonia. The active-site cofactor of the enzyme, termed FeMoco, is unique in nature. It has seven Fe and one Mo atoms connected by S bridges, with a C atom in the center of the cofactor. Another unusual feature is that it has a large homocitrate ligand known to be of importance for catalysis. In the present computational study, the role of the homocitrate ligand is investigated. It is found that a large structural change, which makes Mo-III five coordinated, is energetically favorable in the more reduced states. This is of probable importance for the nitrogenase mechanism.

  • 40.
    Siegbahn, Per E. M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Is there computational support for an unprotonated carbon in the E-4 state of nitrogenase?2018In: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 39, no 12, p. 743-747Article in journal (Refereed)
    Abstract [en]

    In the key enzyme for nitrogen fixation in nature, nitrogenase, the active site has a metal cluster with seven irons and one molybdenum bound by bridging sulfurs. Surprisingly, there is also a carbon in the center of the cluster, with a role that is not known. A mechanism has been suggested experimentally, where two hydrides leave as a hydrogen molecule in the critical E-4 state. A structure with two hydrides, two protonated sulfurs and an unprotonated carbon has been suggested for this state. Rather recently, DFT calculations supported the experimental mechanism but found an active state where the central carbon is protonated all the way to CH3. Even more recently, another DFT study was made that instead supported the experimentally suggested structure. To sort out the origin of these quite different computational results, additional calculations have here been performed using different DFT functionals. The conclusion from these calculations is very clear and shows no computational support for an unprotonated carbon in E-4.

  • 41.
    van der Werf, Angela
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Transformations of Nitrosoarenes and Alkynyl Enones: Selective Synthesis of Nitrogen-Containing Compounds2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The nitrogen atom plays a unique role in organic chemistry. It is abundantly found in organic materials and is responsible for the activity of many biologically relevant compounds. In this thesis, nitrosoarenes and keto- and pyridyl-substituted enynes are used as convenient starting materials for the selective synthesis of nitrogen-containing compounds.

    Nitrosoarenes are versatile compounds that can undergo a broad range of reactions. The nature of the nitroso group is significantly different from that of related nitrogen-based functional groups and this can be used as an advantage in the development of new methodology. In the first part of this thesis, the para-selective halogenation of nitrosoarenes with copper(II) halides as halogenating reagents is explored. The one-pot transformation of the products to the corresponding nitroarenes and anilines is demonstrated. The use of nitrosoarenes for radical N-perfluoroalkylation is presented in the next chapters. N-Perfluoroalkylation is a relatively new field and only a limited number of reagents and substrates have been employed so far. In this thesis, the stable and convenient Langlois reagent was used to achieve selective N-trifluoromethylation of nitrosoarenes to obtain the corresponding hydroxylamines. Longer perfluoroalkyl chains were investigated as well, but the less stable products were defluorinated to form hydroxamic acid derivatives. These products could be reduced to yield perfluoroalkyl amides.

    Keto- and pyridyl-substituted enynes are starting materials designed to undergo cyclization reactions in the presence of a metal catalyst and a nucleophile. This offers the possibility to obtain a variety of more complex molecular structures in a single step. In the second half of the thesis, the reaction between these starting materials and enamines is explored. A range of cyclopenta[c]furans were synthesized in good yields and with high diastereoselectivities from alkynyl enones and enamines with InBr3 as the catalyst. The enamines were formed in situ in a multicomponent reaction. Pyridyl-substituted enynes are the pyridine analogues of alkynyl enones and were found to form polycyclic indolizines in the reaction with cyclic enamines with AgOTf as a catalyst. Good yields and high to excellent diastereoselectivities were obtained. When the reaction was performed with in situ-generated enamines, different indolizine derivatives were obtained.

  • 42.
    Verho, Oscar
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Pourghasemi Lati, Monireh
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Oschmann, Michael
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    A Two-Step Procedure for the Overall Transamidation of 8-Aminoquinoline Amides Proceeding via the Intermediate N-Acyl-Boc-Carbamates2018In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 83, no 8, p. 4464-4476Article in journal (Refereed)
    Abstract [en]

    Herein a two-step strategy for achieving overall transamidation of 8-aminoquinoline amides has been explored. In this protocol, the 8-aminoquinoline amides were first treated with Boc(2)O and DMAP to form the corresponding N-acyl-Boc-carbamates, which were found to be sufficiently reactive to undergo subsequent aminolysis with different amines in the absence of any additional reagents or catalysts. To demonstrate the utility of this approach, it was applied on a number of 8-aminoquinoline amides from the recent C-H functionalization literature, enabling access to a range of elaborate amide derivatives in good to high yields

  • 43.
    Vico Solano, Marta
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    González Miera, Greco
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Pascanu, Vlad
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Inge, A. Ken
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Martín‐Matute, Belén
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Versatile Heterogeneous Palladium Catalysts for Diverse Carbonylation Reactions under Atmospheric Carbon Monoxide Pressure2018In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 10, no 5, p. 1089-1095Article in journal (Refereed)
    Abstract [en]

    Herein, we report a versatile carbonylation protocol using heterogeneous Pd-0 nanoparticles supported on the metal-organic frameworks (MOFs) MIL-88B-NH2 (Fe/Cr). The synthesis of a vast array of carbonyls, which includes amides, esters, carboxylic acids, and -ketoamides, was achieved through mono- and dicarbonylation reactions. The selectivity could be controlled simply by tuning the reaction conditions. Superior activity and selectivity were recorded in some cases compared to that achieved with commercial Pd/C. However, the utility of an elaborate catalyst support is questionable and important reactivity and recyclability issues are discussed.

  • 44.
    Villo, Piret
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry. University of Tartu, Estonia.
    Kervefors, Gabriella
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Olofsson, Berit
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Inside front cover2018Other (Other academic)
  • 45.
    Wang, Dong
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    de Wit, Martin J. M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis of Densely Substituted Conjugated Dienes by Transition-Metal-Free Reductive Coupling of Allenylboronic Acids and Tosylhydrazones2018In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 83, no 15, p. 8786-8792Article in journal (Refereed)
    Abstract [en]

    Tosylhydrazones and allenylboronic acids underwent a transition-metal-free reductive coupling reaction. This process is suitable for synthesis of tetra- and pentasubstituted conjugated dienes. The corresponding allenyl-Bpin substrate showed a very poor reactivity. The reaction is suggested to involve coupling of the in situ formed diazo compound and allenylboronic acid. The intermediate formed in this coupling undergoes allenyl migration followed by protodeboronation to furnish a conjugated diene as major product.

  • 46.
    Yang, Bin
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Qiu, Youai
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Control of Selectivity in Palladium(II)-Catalyzed Oxidative Transformations of Allenes2018In: Accounts of Chemical Research, ISSN 0001-4842, E-ISSN 1520-4898, Vol. 51, no 6, p. 1520-1531Article, review/survey (Refereed)
    Abstract [en]

    Oxidation reactions play a central role in organic synthesis, and it is highly desirable that these reactions are mild and occur under catalytic conditions. In Nature, oxidation reactions occur under mild conditions via cascade processes, and furthermore, they often occur in an enantioselective manner with many of them involving molecular oxygen or hydrogen peroxide as the terminal oxidant. Inspired by the reactions in Nature, we have developed a number of Pd(II)-catalyzed cascade reactions under mild oxidative conditions. These reactions have an intrinsic advantage of step economy and rely on selectivity control in each step. In this Account, we will discuss the control of chemo-, regio-, and diastereoselectivity in Pd(II)-catalyzed dehydrogenative cascade coupling reactions. The enantioselective version of this methodology has also been addressed, and new chiral centers have been introduced using a catalytic amount of a chiral phosphoric acid (CPA). Research on this topic has provided access to important compounds attractive for synthetic and pharmaceutical chemists. These compounds include carbocyclic, heterocyclic, and polycyclic systems, as well as polyunsaturated open-chain structures. Reactions leading to these compounds are initiated by coordination of an allene and an unsaturated pi-bond moiety, such as olefin, alkyne, or another allene, to the Pd(II) center, followed by allene attack involving a C(sp(3))-H cleavage under mild reaction conditions. Recent progress within our research group has shown that weakly coordinating groups (e.g., hydroxyl, alkoxide, or ketone) could also initiate the allene attack on Pd(II), which is essential for the oxidative carbocyclization. Furthermore, a highly selective palladium-catalyzed allenic C(sp(3))-H bond oxidation of allenes in the absence of an assisting group was developed, which provides a novel and straightforward synthesis of [3]dendralene derivatives. For the oxidative systems, benzoquinone (BQ) and its derivatives are commonly used as oxidants or catalytic co-oxidants (electron transfer mediators, ETMs) together with molecular oxygen. A variety of transformations including carbocyclization, acetoxylation, arylation, carbonylation, borylation, beta-hydride elimination, alkynylation, alkoxylation, and olefination have been demonstrated to be compatible with this Pd(II)-based catalytic oxidative system. Recently, several challenging synthetic targets, such as cyclobutenes, seven-membered ring carbocycles, spirocyclic derivatives, functional cyclohexenes, and chiral cyclopentenone derivatives were obtained with high selectivity using these methods. The mechanisms of the reactions were mainly studied by kinetic isotope effects (KIEs) or DFT computations, which showed that in most cases the C(sp(3))-H cleavage is the rate-determining step (RDS) or partially RDS. This Account will describe our efforts toward the development of highly selective and atom-economic palladium(II)-catalyzed oxidative transformation of allenes (including enallenes, dienallenes, bisallenes, allenynes, simple allenes, and allenols) with a focus on overcoming the selectivity problem during the reactions.

  • 47.
    Yuan, Ning
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Swedish University of Agricultural Sciences, Sweden.
    Pascanu, Vlad
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Huang, Zhehao
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Valiente, Alejandro
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Heidenreich, Niclas
    Leubner, Sebastian
    Inge, Andrew Kentaro
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Gaar, Jakob
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Stock, Norbert
    Persson, Ingmar
    Martín-Matute, Belén
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Zou, Xiaodong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Probing the Evolution of Palladium Species in Pd@MOF Catalysts during the Heck Coupling Reaction: An Operando X-ray Absorption Spectroscopy Study2018In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 140, no 26, p. 8206-8217Article in journal (Refereed)
    Abstract [en]

    The mechanism of the Heck C-C coupling reaction catalyzed by Pd@MOFs has been investigated using operando X-ray absorption spectroscopy (XAS) and powder X-ray diffraction (PXRD) combined with transmission electron microscopy (TEM) analysis and nuclear magnetic resonance (H-1 NMR) kinetic studies. A custom-made reaction cell was used, allowing operando PXRD and XAS data collection using high-energy synchrotron radiation. By analyzing the XAS data in combination with ex situ studies, the evolution of the palladium species is followed from the as-synthesized to its deactivated form. An adaptive reaction mechanism is proposed. Mononuclear Pd(II) complexes are found to be the dominant active species at the beginning of the reaction, which then gradually transform into Pd nanoclusters with 13-20 Pd atoms on average in later catalytic turnovers. Consumption of available reagent and substrate leads to coordination of Cl- ions to their surfaces, which causes the poisoning of the active sites. By understanding the deactivation process, it was possible to tune the reaction conditions and prolong the lifetime of the catalyst.

  • 48. Zerbetto, Mirco
    et al.
    d'Ortoli, Thibault Angles
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Polimeno, Antonino
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Differential Dynamics at Glycosidic Linkages of an Oligosaccharide as Revealed by C-13 NMR Spin Relaxation and Stochastic Modeling2018In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 122, no 8, p. 2287-2294Article in journal (Refereed)
    Abstract [en]

    Among biomolecules, carbohydrates are unique in that not only can linkages be formed through different positions, but the structures may also be branched. The trisaccharide beta-D-Glcp-(1 -> 3)[beta-D-Glcp-(1 -> 2)]-alpha-D-Manp-OMe represents a model of a branched vicinally disubstituted structure. A C-13 site -specific isotopologue, with labeling in each of the two terminal glucosyl residues, enabled the acquisition of high-quality C-13 NMR relaxation parameters, T-1 and T-2, and heteronuclear NOE, with standard deviations of <= 0.5%. For interpretation of the experimental NMR data, a diffusive chain model was used, in which the dynamics of the glycosidic linkages is coupled to the global reorientation motion of the trisaccharide. Brownian dynamics simulations relying on the potential of mean force at the glycosidic linkages were employed to evaluate spectral densities of the spin probes. Calculated NMR relaxation parameters showed a very good agreement with experimental data, deviating <3%. The resulting dynamics are described by correlation times of 196 and 174 ps for the beta-(1 -> 2)- and beta-(1 -> 3)-linked glucosyl residues, respectively, i.e., different and linkage dependent. Notably, the devised computational protocol was performed without any fitting of parameters.

  • 49.
    Zhao, Jian
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Jonker, Sybrand J. T.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Meyer, Denise N.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Schulz, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Tran, C. Duc
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Eriksson, Lars
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Szabó, Kálmán J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Copper-catalyzed synthesis of allenylboronic acids. Access to sterically encumbered homopropargylic alcohols and amines by propargylboration2018In: Chemical Science, ISSN 2041-6520, E-ISSN 2041-6539, Vol. 9, no 13, p. 3305-3312Article in journal (Refereed)
    Abstract [en]

    Tri- and tetrasubstituted allenylboronic acids were prepared via a new versatile copper-catalyzed methodology. The densely functionalized allenylboronic acids readily undergo propargylboration reactions with ketones and imines without any additives. Catalytic asymmetric propargylborylation of ketones is demonstrated with high stereoselectivity allowing for the synthesis of highly enantioenriched tertiary homopropargyl alcohols. The reaction is suitable for kinetic resolution of racemic allenylboronic acids affording alkynes with adjacent quaternary stereocenters.

1 - 49 of 49
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