| 1. |
- Lundgren, Stina, et al.
(författare)
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Micro reactors for the optimisation of reaction conditions in asymmetric metal catalysis
- 2005
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Ingår i: Micro Total Analysis Systems 2004. - 0854046437 ; , s. 445-447
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Konferensbidrag (refereegranskat)abstract
- Two types of micro reactors were employed for enantioselective metal catalysed reactions. In the first type of reactor, an electroosmotic flow was used, whereas the second type of reactor used a pressure driven flow. The purpose of the study is to develop tools for rapid and efficient optimization of reactions, utilising minimum amounts of reagents.
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| 2. |
- Belda, O., et al.
(författare)
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Bispyridylamides - coordination chemistry and applications in catalytic reactions
- 2005
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Ingår i: Coordination chemistry reviews. - : Elsevier BV. - 0010-8545 .- 1873-3840. ; 249:06-maj, s. 727-740
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Forskningsöversikt (refereegranskat)abstract
- Complexes of bis(2-pyridylamides) with most metal ions have been described. A variety of coordination modes, with the neutral or the deprotonated amide functions binding either via the carbonyl oxygen atom or the amide nitrogen atom have been identified. The modular technique used for the preparation of the compounds permits facile access to ligands with substituted pyridine nuclei and ligands with different backbones. Moreover, symmetric as well as asymmetric compounds, with equal or different pyridine rings and with symmetric or non-symmetric amines, can conveniently be prepared. Chiral derivatives are easily obtained starting from chiral diamines. Several metal complexes have been studied as mimics of biological systems. In recent years a variety of metal complexes have also been employed in catalysis. Oxidations of alkanes and alkenes have been particularly well studied, although modest reactivity has usually been encountered. Other applications include their use as ligands in Lewis acid catalyzed processes. Recently, it was shown that complexes with molybdenum catalyze highly regio- and enantioselective allylic alkylations.
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| 3. |
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| 4. |
- Del Litto, Raffaella, et al.
(författare)
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Carbohydrate-Based Pyridine-2-carboxamides for Mo-Catalyzed Asymmetric Allylic Alkylations
- 2009
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Ingår i: European Journal of Organic Chemistry. - : Wiley. - 1434-193X .- 1099-0690. ; :9, s. 1352-1356
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Tidskriftsartikel (refereegranskat)abstract
- Bis(pyridine-2-carboxamides) were prepared from 1,2-diamines obtained from alpha-D-ghlcose and alpha-D-mannose. The ligands were assessed in molybdenum-catalyzed asymmetric allylic alkylations (AAA) by using both methyl (E)-3-phenyl-2-propenyl and methyl rac-1-phenyl-2-propenyl carbonates and dimethyl malonate as nucleophile under microwave irradiation. High enantioselectivity (99 % ee) and high regioselectivity (49:1 in favour of the branched isomer) were observed in reactions of the linear achiral substrate in the presence of 10 mol-% of a catalyst prepared from a ligand derived from glucose. Somewhat lower enantioselectivity (up to 96 % ee) was observed in reactions with the branched racemic carbonate by using the same ligand. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
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| 5. |
- Durieux, Guillaume, et al.
(författare)
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Rate and Mechanism of the Oxidative Addition of a Silylborane to Pt0 Complexes : Mechanism for the Pt-Catalyzed Silaboration of 1,3-Cyclohexadiene
- 2008
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Ingår i: European Journal of Inorganic Chemistry. - Weinheim : Wiley-VCH. - 1434-1948 .- 1099-1948 .- 1099-0682. ; :27, s. 4236-4241
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Tidskriftsartikel (refereegranskat)abstract
- The chemical reduction of Pt(acac)(2) by DIBALH in the presence of phosphanes, which is used to generate active Pt-0 complexes in the Pt-catalyzed silaboration of cyclohexadiene by 2-(diinethylphenylsilyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (1) leading to the 1,4-silaborated product, was mimicked by the electrochemical reduction of Pt(acac)(2) in the presence of 2 equiv. of PR3 (R = Ph, nBu). The electrochemical reduction generates free acac anions and neutral Pt-0-(PR3)(2) complexes. The kinetics of the oxidative addition of bromobenzene (used first as a model molecule) and silylborane 1 to the Pt-0 complexes was investigated and the rate constants determined. Pt-0(PnBu(3))(2) is much more reactive than Pt-0(PPh3)(2) towards 1. From the electrochemical study, it emerges that the acac anions released in the reduction of Pt(acac)(2) do not coordinate to the Pt-0(PR3)(2) complexes. Consequently, the rate of the oxidative addition of 1 to Pt-0(PR3)(2), generated either by the electrochemical reduction or by the chemical reduction by DIBALH, is not affected by the acac anions and a posteriori not by aluminum cations. The oxidative addition and the further step of the catalytic cycle [insertion of the diene into the Pt-B bond of the Si-Pt-B complex generated in the oxidative addition, with formation of the eta(3)-allyl)Pt-Si complex] were monitored by NMR spectroscopy. Pt-0 and Pt-II complexes involved in the catalytic cycle were characterized. The oxidative addition is faster when the ligand is PMe2Ph relative to that obtained with PPh3, in agreement with the electrochemical data. No reductive elimination within the ((eta(3)-allyl))Pt-Si complex is observed when the ligand is PMe2Ph, whereas reactions in the presence of PPh3 proceeded to give the final product. As a consequence, PPh3 is a better ligand than PMe2Ph for the catalytic reaction, as observed experimentally.
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| 6. |
- Engqvist, Magnus, 1973-
(författare)
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Direct Amino Acid-Catalyzed Enantioselective α-Oxidation Reactions and Asymmetric de novo Synthesis of Carbohydrates
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The ability of amino acids to form nucleophilic enamines with aldehydes and ketones has been used in the development of asymmetric α-oxidation reactions with electrophilic oxidizing agents. Singlet molecular oxygen has for the first time been asymmetrically incorporated into aldehydes and ketones, and the products were isolated as their corresponding diols in good yields and ee’s. Organocatalytic α-oxidations of cyclic ketones with iodosobenzene and N-sulfonyloxaziridine were also possible and furnished after reduction the product diols in generally low yields and in low to good ee’s. Amino acids have also been shown to catalyze the formation of carbohydrates by sequential aldol reactions. For example, proline and hydroxy proline mediate a highly selective trimerisation of α-benzyloxyacetaldehyde into allose, which was obtained in >99 % ee. Non linear effect studies of this reaction revealed the largest permanent nonlinear effect observed in a proline-catalyzed reaction to date. Moreover, polyketides were also assembled in a similar fashion by an amino acid-catalyzed one-pot reaction, and was successful for the trimerisation of propionaldehyde, however the sequential cross aldol reactions suffered from lower selectivities. This problem was overcome by the development of a two-step synthesis that enabled the formation of a range of polyketides with excellent selectivities from a variety of aldehydes. The method furnishes the polyketides via the shortest route reported and in comparable product yields to most multi-step synthesis. All polyketides were isolated as single diastereomers with >99 % ee. Based on the observed amino acid-catalysis, amino acids are thought to have taken part in the prebiotic formation of tetroses and hexoses.
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| 7. |
- Eriksson, Carina, 1973-
(författare)
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Isolation, Synthesis and Structure-Activity Relationships of Antifeedants against the Pine Weevil, Hylobius Abietis
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The large pine weevil, Hylobius abietis L., is a major insect pest on conifer seedlings in northern Europe. Due to its feeding newly planted trees get girdled, resulting in high seedling mortality (up to 80%). As a consequence great financial losses to the forest industry occur. Today the seedlings are protected with the pyrethroid insecticide cypermethrin. This insecticide is toxic to aquatic organisms and is, from 2010, prohibited for use in Sweden by the Swedish Chemicals Inspectorate. An alternative to insecticides is to protect the seedlings with antifeedants, compounds that, either through taste or smell or both, deter the weevils from feeding. This thesis describes the search for and the synthesis of such antifeedant compounds. Bark extracts of several woody species, known to be non-palatable to the weevil, were prepared and found to display antifeedant activity against H. abietis. The major chemical constituents of the extracts were tested for antifeedant activity. Antifeedants such as eugenol, 2-phenylethanol and benzylalcohol, but also feeding stimulants such as β-sitosterol and linoleic acid, were identified. An extract of linden bark, Tilia cordata, was shown to contain nonanoic acid, a highly active antifeedant. Other aliphatic carboxylic acids were also found to display high antifeedant activities against the weevil, both in laboratory and in field tests. The enantiomers of dihydropinidine, a piperidine alkaloid present in several conifer species, were prepared by dimethylzinc mediated allylation of 2- methyltetrahydropyridine-N-oxide. When tested in micro feeding assays, no difference in antifeedant activity was found for the enantiomers. In a field test high antifeedant activity, comparable with that of the presently used insecticide cypermethrin, was found for (±)-dihydropindine. Other naturally occurring piperidine alkaloids were synthesised and also found to display high antifeedant activities in laboratory tests. Structure-activity relationships were evaluated for methoxy substituted benzaldehydes, benzoic acids and cinnamic aldehydes, -acids, -esters and -alcohols. While the carboxylic acids were inactive or even feeding stimulants, the aldehydes were the most active antifeedants
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| 8. |
- Fjellander, Ester, 1982-, et al.
(författare)
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Atropoisomerism in Phosphepines and Azepines
- 2009
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Ingår i: Journal of Organic Chemistry. - Washington DC : American Chemical Society. - 0022-3263 .- 1520-6904. ; 74:23, s. 9120-9125
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Tidskriftsartikel (refereegranskat)abstract
- Free energy barriers to biaryl tropoinversion in metal complexes with tropos phosphepine and azepine ligands were determined by temperature-dependent P-31 NMR inversion-transfer experiments and line shape analysis of the temperature-dependent H-1 NMR spectra, respectively. The barrier in the PdCl2 complex of the azepine ligand was found to be slightly higher than that of the corresponding free ligand. Studies of a tridentate azepine ligand Suggested that Configurational change takes place without prior decoordination from the metal.
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| 9. |
- Forcato, M., et al.
(författare)
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Chiral, enantiopure aluminum(III) and titanium(IV) azatranes
- 2006
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Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1434-1948 .- 1099-1948 .- 1099-0682. ; :5, s. 1032-1040
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Tidskriftsartikel (refereegranskat)abstract
- Al-III and Ti-IV complexes of C-3-symmetric tetradentate trisamidoamme ligands with trigonal bipyramidal coordination geometry, containing chlorine or dialkylamido groups, or with a free coordination site in the apical position, have been synthesised by salt metathesis and amine elimination. Products with threefold symmetry were generally obtained for tetravalent titanium, whereas for the aluminium complexes either asymmetric structures with two of the three podand arms taking part in coordination to the metal or symmetric arrangements possessing the full threefold symmetry were formed depending on the steric properties of the ligands.
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| 10. |
- Frölander, Anders, et al.
(författare)
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Ag+-Assisted Hydrosilylation : Complementary Behavior of Rh and Ir Catalysts (Reversal of Enantioselectivity)
- 2007
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Ingår i: Organic Letters. - : American Chemical Society (ACS). - 1523-7060 .- 1523-7052. ; 9:7, s. 1371-1374
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Tidskriftsartikel (refereegranskat)abstract
- The presence of a suitably situated hydroxy function in a PHOX ligand leads to an enhancement of the enantioselectivity in Rh-catalyzed hydrosilylations of prochiral ketones in the presence of AgBF4 (95% ee for acetophenone as compared to 75% using i-Pr-phosphinooxazoline (PHOX)). Exchanging Rh for Ir affords the product with the opposite absolute configuration (78% ee).
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