| 1. |
- Ambrogio, IIaria, et al.
(author)
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Unusual Selectivity-Determining Factors in the Phosphine-Free Heck Arylation of Allyl Ethers
- 2008
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In: Organometallics. - : American Chemical Society (ACS). - 0276-7333 .- 1520-6041. ; 27
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Journal article (peer-reviewed)abstract
- The Heck reaction of aryl iodides and bromides with allyl ethers has been investigated. Using phosphine-free Pd(OAc)2 in DMF at 90 °C in the presence of Bu4NOAc, the reaction gave cinnamyl derivatives, usually in good to high yields, with a wide range of aryl halides. The reaction tolerates a variety of functional groups, including ether, amide, alcohol, aldehyde, ketone, ester, cyano, carboxylic acid, and nitro groups. Ortho-substituted arylating agents afforded moderate yields in some cases, though good to high yields were obtained with o-iodotoluene, iodovanillin, and 1-iodonaphthalene. Several pieces of experimental evidence suggest that the observed selectivity in formation of the vinylic substitution products is kinetic in origin under these conditions. A DFT investigation has been performed to clarify the source of product selectivity and, in particular, the preference for cinnamyl ether over enol ether products. Interestingly, it was found that the product selectivity does not arise from competing β-hydride eliminations but rather from a competition between β-elimination and hindered single-bond rotation in the initial carbopalladation product.
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| 2. |
- Bantreil, Xavier, et al.
(author)
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γ- and δ-lactams through palladium-catalyzed intramolecular allylic alkylation: enantioselective synthesis, NMR Investigation, and DFT rationalization.
- 2011
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In: Chemistry - A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 17:10, s. 2885-96
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Journal article (peer-reviewed)abstract
- The Pd-catalyzed intramolecular allylic alkylation of unsaturated amides to give γ- and δ-lactams has been studied in the presence of chiral ligands. Ligand (R)-3,5-tBu-MeOBIPHEP (MeOBIPHEP = 6,6'-dimethoxybiphenyl-2,2-diyl)bis(diphenylphosphine)) afforded the best results and allowed the cyclization reactions to take place in up to 94:6 enantiomeric ratio. A model Pd-allyl complex has been prepared and studied through NMR spectroscopic analysis, which provided insight into the processes responsible for the observed enantiomeric ratios. DFT studies were used to characterize the diastereomeric reaction pathways. The calculated energy differences were in good agreement with the experimentally observed enantiomeric ratios.
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| 3. |
- Fristrup, Peter, et al.
(author)
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On the Nature of the Intermediates and the Role of Chloride Ions in Pd-Catalyzed Allylic Alkylations : Added Insight from Density Functional Theory
- 2008
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In: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 112:50, s. 12862-12867
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Journal article (peer-reviewed)abstract
- The reactivity of intermediates in palladium-catalyzed allylic alkylation was investigated using DFT (B3LYP) calculations including a PB-SCRF solvation model. In the presence of both phosphine and chloride ligands, the allyl intermediate is in equilibrium between a cationic eta(3)-allylPd complex with two phosphine ligands, the corresponding neutral complex with one phosphine and one chloride ligand, and a neutral eta(1)-allylPd complex with one chloride and two phosphine ligands. The eta(1)-complex is unreactive toward nucleophiles. The cationic eta(3)-complex is the intermediate most frequently invoked in the title reaction, but in the presence of halides, the neutral, unsymmetrically substituted eta(3)-CoMplex will be formed rapidly from anionic Pd(0) complexes in solution. Since the latter will prefer both leaving group ionization and reaction with nucleophiles in the position trans to phosphorus, it can rationalize the observed "memory effect" (a regioretention) in the title reaction, even in the absence of chiral ligands.
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| 4. |
- Fristrup, Peter, et al.
(author)
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The Mechanism for the Rhodium-Catalyzed Decarbonylation of Aldehydes: A Combined Experimental and Theoretical Study
- 2008
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In: J.Am.Chem.Soc.. - : American Chemical Society (ACS). ; 130, s. 5206-5215
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Journal article (peer-reviewed)abstract
- The mechanism for the rhodium-catalyzed decarbonylation of aldehydes was investigated by experimental techniques (Hammett studies and kinetic isotope effects) and extended by a computational study (DFT calculations). For both benzaldehyde and phenyl acetaldehyde derivatives, linear Hammett plots were obtained with positive slopes of +0.79 and +0.43, respectively, which indicate a buildup of negative charge in the selectivity-determining step. The kinetic isotope effects were similar for these substrates (1.73 and 1.77 for benzaldehyde and phenyl acetaldehyde, respectively), indicating that similar mechanisms are operating. A DFT (B3LYP) study of the catalytic cycle indicated a rapid oxidative addition into the C(O)−H bond followed by a rate-limiting extrusion of CO and reductive elimination. The theoretical kinetic isotope effects based on this mechanism were in excellent agreement with the experimental values for both substrates, but only when migratory extrusion of CO was selected as the rate-determining step.
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| 5. |
- Runarsson, Ögmundur, et al.
(author)
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Resolution and Determination of the Absolute Configuration of a Twisted Bis-Lactam Analogue of Tröger's Base: A Comparative Spectroscopic and Computational Study.
- 2015
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In: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 1520-6904 .- 0022-3263. ; 80:16, s. 8142-8149
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Journal article (peer-reviewed)abstract
- The first reported twisted bis-lactam, a racemic Tröger's base (TB) analogue (2), was resolved into its enantiomers on a chiral stationary phase HPLC column. The absolute configuration of (+)-2 was determined to be (R,R)-2 by comparing experimental and calculated vibrational circular dichroism (VCD) and electronic circular dichroism (ECD) spectra. The absolute configuration of (-)-2 was determined by comparing experimental and calculated electronic circular dichroism (ECD) spectra. The corresponding theoretical spectra were calculated using the lowest energy conformation of (R,R)-2 and (S,S)-2 at the B3LYP/6-31G(d,p) level of theory. The absolute configuration of (+)-2 was also determined to (R,R)-2 by anomalous X-ray diffraction (AXRD) in a chiral space group P212121 using Cu-irradiation resulting in a very low Flack parameter of -0.06(3), despite the heaviest element being an oxygen atom, thus unambiguously confirming the results from the spectroscopic studies. We conclude that, for the Tröger's base (TB) analogue (2), we may rank the reliability of the individual methods for AC determination as AXRD ≫ VCD > ECD, while the synergy of all three methods provides very strong confidence in the assigned ACs of (+)-(R,R)-2 and (-)-(S,S)-2.
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| 6. |
- Svensen, Nina, et al.
(author)
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Memory Effects in Palladium-Catalyzed Allylic Alkylations of 2-Cyclohexen-1-yl Acetate
- 2007
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In: Adv.Synth.Catal. - : Wiley. ; 349, s. 2631-2640
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Journal article (peer-reviewed)abstract
- The objective of this work was to characterize the enantiospecificity of the allylic alkylation of enantioenriched 2-cyclohexen-1-yl acetate with the enolate ion of dimethyl malonate catalyzed by unsymmetrical palladium catalysts. The precatalysts employed were (3-allyl)PdLCl, where L is a monophosphine ligand [PPh3, PCy3, P(2-BiPh)Cy2, or P(t-Bu)3], all of which afforded enantiospecificity to some extent (5-47 %). Quantum mechanical calculations show that, theoretically, the enantiospecificity should be high due to a preference for the trans to P transition state in both formation of the 3-allyl intermediate and nucleophilic attack. However, the observed enantiospecificity is relatively low due to isomerization of the 3-allyl intermediate and/or dynamic equilibria between the catalytically active (3-allyl)PdLCl species and [(3-allyl)PdL2]+ or [(3-allyl)PdCl]2. It was also observed experimentally that increasing the bulk of the phosphine inhibits formation of the [(3-allyl)PdL2]+ complexes, significantly increasing the observed enantiospecificity for some of the ligands.
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| 7. |
- van der Heijde, Nicky, et al.
(author)
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Use and outcome of minimally invasive pancreatic surgery in the European E-MIPS registry
- 2023
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In: HPB. - : ELSEVIER SCI LTD. - 1365-182X .- 1477-2574. ; 25:4, s. 400-408
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Journal article (peer-reviewed)abstract
- Background: The European registry for minimally invasive pancreatic surgery (E-MIPS) collects data on laparoscopic and robotic MIPS in low-and high-volume centers across Europe.Methods: Analysis of the first year (2019) of the E-MIPS registry, including minimally invasive distal pancreatectomy (MIDP) and minimally invasive pancreatoduodenectomy (MIPD). Primary outcome was 90-day mortality.Results: Overall, 959 patients from 54 centers in 15 countries were included, 558 patients underwent MIDP and 401 patients MIPD. Median volume of MIDP was 10 (7-20) and 9 (2-20) for MIPD. Median use of MIDP was 56.0% (IQR 39.0-77.3%) and median use of MIPD 27.7% (IQR 9.7-45.3%). MIDP was mostly performed laparoscopic (401/558, 71.9%) and MIPD mostly robotic (234/401, 58.3%). MIPD was performed in 50/54 (89.3%) centers, of which 15/50 (30.0%) performed >= 20 MIPD annually. This was 30/ 54 (55.6%) centers and 13/30 (43%) centers for MIPD respectively. Conversion rate was 10.9% for MIDP and 8.4% for MIPD. Overall 90 day mortality was 1.1% (n = 6) for MIDP and 3.7% (n = 15) for MIPD.Conclusion: Within the E-MIPS registry, MIDP is performed in about half of all patients, mostly using laparoscopy. MIPD is performed in about a quarter of patients, slightly more often using the robotic approach. A minority of centers met the Miami guideline volume criteria for MIPD.
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| 8. |
- Wixe, Torbjörn, et al.
(author)
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A short designed semi-aromatic organic nanotube - synthesis, chiroptical characterization, and host properties.
- 2014
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In: Organic and Biomolecular Chemistry. - : Royal Society of Chemistry (RSC). - 1477-0539. ; 12:44, s. 8930-8941
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Journal article (peer-reviewed)abstract
- The first generation of an organic nanotube based on the enantiomerically pure bicyclo[3.3.1]nonane framework is presented. The helical tube synthesised is the longest to date having its aromatic systems oriented parallel to the axis of propagation (length ∼26 Å and inner diameter ∼11 Å according to molecular dynamics simulations in chloroform). The synthesis of the tube, a heptamer, is based on a series of Friedländer condensations and the use of pyrido[3,2-d]pyrimidine units as masked 2-amino aldehydes, as a general means to propagate organic tubular structures and the introduction of a methoxy group for modification toward solubility and functionalization are described. The electronic CD spectra of the tube and molecular intermediates are correlated with theoretical spectra calculated with time-dependent density functional theory to characterize the chirality of the tube. Both experimental (NMR-titrations) and theoretical (molecular dynamics simulations) techniques are used to investigate the use of the tube as a receptor for the acetylcholine and guanidinium cations, respectively.
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| 9. |
- Wixe, Torbjörn, et al.
(author)
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Synthesis of an Orthogonal Topological Analogue of Helicene.
- 2013
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In: Chemistry: A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 19:44, s. 14963-14969
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Journal article (peer-reviewed)abstract
- The synthesis of an orthogonal topological pentamer analogue of helicene is presented. This analogue forms a tubular structure with its aromatic systems directed parallel to the axis of propagation, which creates a cavity with the potential to function as a host molecule. The synthetic strategy reported, based on a series of repeating Friedländer condensations that utilize pyrido[3,2-d]pyrimidine moieties as protected amino aldehydes, allows for the facile access of higher generations of helical, tubular structures. As a result of the synthetic strategy, only a helical isomer of the pentamer is possible. The structure and absolute configuration of the pentamer were elucidated from a combination of NMR spectroscopic data, optical properties, X-ray structures, and by comparison of an experimental electronic circular dichroism spectrum to a calculated spectrum.
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