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| 2. |
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| 3. |
- Gøgsig, Thomas M, et al.
(författare)
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Mild and efficient nickel-catalyzed Heck reactions with electron-rich olefins.
- 2012
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 134:1, s. 443-52
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Tidskriftsartikel (refereegranskat)abstract
- A new efficient protocol for the nickel-catalyzed Heck reaction of aryl triflates with vinyl ethers is presented. Mild reaction conditions that equal those of the corresponding palladium-catalyzed Heck reaction are applied, representing a practical and more sustainable alternative to the conventional regioselective arylation of vinyl ethers. A catalytic system comprised of Ni(COD)(2) and 1,1'-bis(diphenylphosphino)ferrocene (DPPF) in combination with the tertiary amine Cy(2)NMe proved effective in the olefination of a wide range of aryl triflates. Both electron-deficient and electron-rich arenes proved compatible, and the corresponding aryl methyl ketone could be secured after hydrolysis in yields approaching quantitative. Good functional group tolerance was observed matching the characteristics of the analogous Pd-catalyzed Heck reaction. The high levels of catalytic activity were explained by the intermediacy of a cationic nickel(II) complex potentially responsible for the successive β-hydride elimination and base promoted catalyst regeneration. Although these elementary reactions are normally considered challenging, DFT calculations suggested this pathway to be favorable under the applied reaction conditions.
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| 4. |
- Lennernäs, Bo, 1963, et al.
(författare)
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Hypofractionation for radiotherapy of prostate cancer using a low alfa/beta ratio--possible reasons for concerns? An example of five dimensional radiotherapy.
- 2011
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Ingår i: Acta oncologica (Stockholm, Sweden). - 1651-226X. ; 50 Suppl 1, s. 111-5
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Tidskriftsartikel (refereegranskat)abstract
- It is very attractive, due to the assumed low alfa/beta ratio of prostate cancer (PC), to construct new treatment schedules for prostate cancer using only a few large fractions of radiation (hypofractionation). This will widen the therapeutic window since the ratio for PC might be lower than that of the organs at risk (OAR). PC is an extremely variable disease and often contains both highly and poorly differentiated cells. It is reasonable to assume that different cells have different patterns of radiosensitivity, i.e. alfa/beta ratios and proliferation. In this study we will simulate the effect on the outcome of the treatment with different fractionations and different ratios.
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| 6. |
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| 7. |
- Nilsson Lill, Sten O., 1970, et al.
(författare)
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Application of Q2MM to Stereoselective Reactions
- 2010
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Ingår i: Current Organic Chemistry. - : Wiley. - 1385-2728. ; 14:15, s. 1629-1645
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Tidskriftsartikel (refereegranskat)abstract
- Q2MM is a method designed to allow application of molecular mechanics calculations to transition states in chemical reactions. It is one of the few methods available that allow determination of a complete set of low-energy transition states for medium-sized systems, and thereby gives a unique opportunity to investigate kinetic selectivity, in particular stereoselectivity. The current review will give an outline of the procedure, an overview of the types of reactions that have been studied using this method, and summarize the factors affecting the accuracy of the results.
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| 8. |
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| 9. |
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| 10. |
- Nilsson Lill, Sten O., 1970
(författare)
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Computational Perspectives on Organolithiums
- 2014
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Ingår i: Lithium Compounds in Organic Synthesis: From Fundamentals to Applications. - Weinheim, Germany : Wiley. ; 9783527333431, s. 33-52
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Bokkapitel (refereegranskat)
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| 11. |
- Nilsson Lill, Sten O., 1970, et al.
(författare)
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Development of chiral catalysts for stereoselective synthesis by deprotonations - Experimentation in interplay with computational chemistry
- 2004
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Ingår i: Advances in Quantum Chemistry, Vol 47. - : Elsevier. - 0065-3276 .- 2162-8815. ; 47, s. 1-22
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Tidskriftsartikel (refereegranskat)abstract
- Results are presented advancing the application of quantum chemistry in the field of organic synthesis. Computational chemistry in interplay with experimental chemistry has been given a key role in the development of stereoselective synthesis. Novel molecular systems are being created for catalytic stereoselective deprotonations, a reaction type useful for synthesizing many new compounds, e.g., some having important biological activities. Problems met in this approach to design catalysts and their solutions are presented.
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| 12. |
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| 13. |
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| 14. |
- Nilsson Lill, Sten O., 1970
(författare)
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On the Dimerization of Chlorophyll in Photosystem II
- 2011
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 13:35, s. 16022-16027
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: In photosystem II, absorbed light energy is transferred to a reaction centre consisting of chlorophyll units. Release of an electron from the reaction centre is the starting point for the charge separation and electron transport chain in PSII. Crystal structures of the reaction centre have identified two chlorophyll monomers forming a dimer with a partial structural overlap, thus being stabilized by van der Waals interactions. However, the magnitude of this interaction is not accurately known. In this work, the structure of the chlorophyll dimer has been optimized for the first time using dispersion-corrected density functional theory (B3LYP-DCP) revealing the magnitude of dimerization to be approximately -17 kcal mol(-1). The dispersion interaction is shown to be of great significance for the chlorophyll dimer stabilization. In addition, the redox potential of the chlorophyll dimer is calculated to be 1283 mV in good agreement with recent experimental data.
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| 15. |
- Nilsson Lill, Sten O., 1970, et al.
(författare)
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tBu or not tBu?
- 2012
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539. ; 18:6, s. 1640-9
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Tidskriftsartikel (refereegranskat)abstract
- The regioselectivity in the palladium-catalyzed Heck coupling reaction between an aryl halide and ethyl vinyl ether with four different phosphine ligands: PPh(n)tBu(m) (n=0-3, m=3-n) has been investigated both experimentally and computationally. A zigzag selectivity pattern was experimentally observed upon consecutive replacement of Ph by tBu in the phosphine ligand. Use of a standard DFT method (B3LYP) was shown to give a correct prediction of product preference. However, the trend in relative selectivity among the different ligands could not be correctly described. The use of a more recent DFT functional (M06) parameterized to reproduce dispersion interactions resulted in an improved description. For the sterically most demanding ligands, PtBu(3) and PPhtBu(2), unexpectedly large deviations between experimental and M06 calculated selectivities raised the question of an alternative mechanism for these ligands. In the case of PtBu(3) it was found, in agreement with literature data, that the phosphine ligand could be replaced by a second halide ligand, resulting in an anionic mechanism, with a calculated selectivity in excellent agreement with experimental data. For the PPhtBu(2) ligand, two mechanisms are suggested to operate in parallel, as demonstrated both by computational studies and experimental observation of halide-dependent selectivity. A Halpern effect is observed for all phosphine ligands investigated, that is, the least stable pre-complex results in the most abundant product.
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| 16. |
- Raja, Erum K., et al.
(författare)
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Friedel-Crafts Acylation with Amides
- 2012
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 77:13, s. 5788-5793
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: Friedel-Crafts acylation has been known since the 1870s, and it is an important organic synthetic reaction leading to aromatic ketone products. Friedel-Crafts acylation is usually performed with carboxylic acid chlorides or anhydrides, while amides are generally not useful substrates in these reactions. Despite being the least reactive carboxylic acid derivative, we have found a series of amides capable of providing aromatic ketones in good yields (55-96%, 17 examples). We propose a mechanism involving diminished C-N resonance through superelectrophilic activation and subsequent cleavage to acyl cations.
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| 17. |
- Raja, E. K., et al.
(författare)
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Friedel-Crafts-type reactions with ureas and thioureas
- 2012
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 48:65, s. 8141-8143
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Tidskriftsartikel (refereegranskat)abstract
- Despite the relatively low reactivities of urea and thiourea functional groups towards nucleophilic attack, we have found conditions in which they are useful substrates in Friedel-Crafts reactions. The Bronsted superacid, triflic acid, promotes these reactions and a mechanism is proposed involving dicationic, superelectrophilic intermediates.
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| 18. |
- Rudbeck, Maria E., et al.
(författare)
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Influence of the Molecular Environment on Phosphorylated Amino Acid Models – A Density Functional Theory Study
- 2012
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Ingår i: Journal of Physical Chemistry – B. - 1520-6106. ; 116:9, s. 2751-2757
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Tidskriftsartikel (refereegranskat)abstract
- A protein environment can affect the structure and charge distribution of substrate molecules. Here, the structure and partial charges were studied for different phosphorylated amino acid models in varying environments using density functional theory. The three systems investigated, acetyl phosphate, methyl phosphate, and p-tolyl phosphate are representative models for aspartyl phosphate, serine or threonine phosphate, and tyrosine phosphate, respectively. Combined with the CPCM continuum model, explicit HF and H2O molecules were added in order to model environmental effects and interactions that may occur in a protein matrix. We show how the different interactions affect the scissile P–O(R) bond and that the elongation can be explained by an anomeric effect. An increasing scissile bond length will result in transfer of negative charge to the leaving group and in a widening of the angle between the terminal oxygens of the phosphate molecule, features that can expose the phosphate group to attacking nucleophiles. Lastly, calculations were performed on the active site of the Ca2+-ATPase E2P intermediate, which provide an example of how a protein environment facilitates the formation of a destabilized ground state.
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| 19. |
- Rönnholm, Petra, 1969, et al.
(författare)
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A computational study of the enantioselective addition of n-BuLi to benzaldehyde in the presence of a chiral lithium N,P amide.
- 2012
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Ingår i: Organic & biomolecular chemistry. - : Royal Society of Chemistry (RSC). - 1477-0520 .- 1477-0539. ; 10:14, s. 2807-2814
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Tidskriftsartikel (refereegranskat)abstract
- In the presence of a chiral lithium N,P amide, alkylation of benzaldehyde results in an enantioselective formation of 1-phenyl-pentanol. This stereoselective addition reaction has herein been studied using dispersion-corrected density functional theory. For five different chiral ligands originating from amino acids the resulting enantioselectivity has been computationally determined and compared with experimentally available enantiomeric ratios (e.r.). In all cases the experimentally preferred enantiomer could be reproduced by the computational model. The selectivity trend among the ligands was found strongly sensitive to the amount of dispersion correction included. The origin of selectivity in the alkylation reaction is found to be composed of many combined interactions. For the most selective ligand 2A the most important factors found, which are favouring the (R)-TS, are a CH-π interaction between benzaldehyde-dimethyl ether (DME), stronger Li-solvation, and Li-π interactions with the phenyl ring in the backbone of the chiral lithium N,P amide. In addition, solvation by the bulk solvent and the size of the substituent on the nitrogen are also found important factors for the enantioselectivity.
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| 20. |
- Rönnholm, Petra, 1969, et al.
(författare)
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Aggregation and Solvation of Chiral N,P-Amide Ligands in Coordinating Solvents: A Computational and NMR Spectroscopic Study
- 2012
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Ingår i: Chempluschem. - : Wiley. - 2192-6506. ; 77:9, s. 799-806
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Tidskriftsartikel (refereegranskat)abstract
- The lithium amides of a series of chiral N,P ligands were studied in solution. This ligand class had been shown previously to give good selectivities in asymmetric alkylation of benzaldehyde. These lithium amides were found to aggregate into dimers with surprisingly strong coordination of phosphorus to lithium. The equilibrium between dimeric forms was found to depend strongly on non-bonded interactions within the solute and between solute and solvent. Only if dispersion and free-energy contributions were scaled to approximately 20?% of the gas-phase values was it possible to reproduce the experimentally observed aggregation preferences. NMR spectroscopic shieldings were calculated and found to correlate well with the experimentally observed shifts. Calculated Li,P couplings were shown to be a sensitive measure of the Li?P distance.
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| 21. |
- Salomone, A., et al.
(författare)
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Direct observation of a lithiated oxirane: A synergistic study using spectroscopic, crystallographic, and theoretical methods on the structure and stereodynamics of lithiated ortho-trifluoromethyl styrene oxide
- 2014
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Ingår i: CHEMICAL SCIENCE. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 5:2, s. 528-538
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Tidskriftsartikel (refereegranskat)abstract
- α-Lithiated epoxides, long considered "fleeting" intermediates in the reactions of epoxides with strong bases, have nowadays proven to be key synthons for asymmetric synthesis. In this study, the solution and the solid state structure of an α-lithiated aryloxirane, namely α-lithiated ortho-trifluoromethyl styrene oxide (1-Li), were determined. Single crystal X-ray diffraction analysis of 1-Li performed at 100 K applying the X-TEMP-2 device revealed a self-assembled heterochiral dimeric structure with a rare central six-membered (O-Li-C)2 planar core, which is unprecedented in Li/oxygen carbenoids. Multinuclear magnetic resonance ( 1H, 13C, 19F, 7Li) studies suggested that 1-Li exists in THF solution as a mixture of two interconverting diastereomeric dimeric aggregates, each one featuring a single σ-contact between lithium and a carbon atom. Line shape analysis provided activation parameters for both the dynamic interconversion of the two dimers and the enantiomerisation of 1-Li, which proved to be mostly entropy controlled. The structural assignment in solution was supported by density functional theory computations through the investigation of conformers of monomeric and dimeric complexes of 1-Li featuring different degrees of specific solvation. A mechanism based on the equilibration of six-membered homo- and heterochiral dimers was proposed to explain the configurational instability exhibited by 1-Li in THF. © 2014 The Royal Society of Chemistry.
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