| 1. |
- Axelsson, Anton, 1991, et al.
(author)
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Asymmetric Synthesis of Dihydropyranones with Three Contiguous Stereocenters by an NHC-Catalyzed Kinetic Resolution
- 2021
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In: European Journal of Organic Chemistry. - : Wiley. - 1434-193X .- 1099-0690. ; 2021:25, s. 3657-3661
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Journal article (peer-reviewed)abstract
- An oxidative NHC-catalyzed kinetic resolution (KR) of racemic mixtures is presented. The developed reaction furnishes tricyclic dihydropyranones with three contiguous stereocenters in excellent dia- and enantioselectivity, with good-to-moderate yields. Mechanistic studies indicate that the rate-determining step of the reaction is the formation of the Breslow intermediate, while the selectivity determining step occurs later in the mechanism. The presented methodology enables rapid synthesis of complex structures in a single step.
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| 2. |
- Barbosa de Mattos, Deise Fernanda, 1985, et al.
(author)
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Covalent incorporation of diphenylanthracene in oxotriphenylhexanoate organogels as a quasi-solid photon upconversion matrix
- 2020
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In: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 153:21
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Journal article (peer-reviewed)abstract
- Triplet-triplet annihilation photon upconversion (TTA-UC) in solid state assemblies are desirable since they can be easily incorporated into devices such as solar cells, thus utilizing more of the solar spectrum. Realizing this is, however, a significant challenge that must circumvent the need for molecular diffusion, poor exciton migration, and detrimental back energy transfer among other hurdles. Here, we show that the above-mentioned issues can be overcome using the versatile and easily synthesized oxotriphenylhexanoate (OTHO) gelator that allows covalent incorporation of chromophores (or other functional units) at well-defined positions. To study the self-assembly properties as well as its use as a TTA-UC platform, we combine the benchmark couple platinum octaethylporphyrin as a sensitizer and 9,10-diphenylanthracene (DPA) as an annihilator, where DPA is covalently linked to the OTHO gelator at different positions. We show that TTA-UC can be achieved in the chromophore-decorated gels and that the position of attachment affects the photophysical properties as well as triplet energy transfer and triplet-triplet annihilation. This study not only provides proof-of-principle for the covalent approach but also highlights the need for a detailed mechanistic insight into the photophysical processes underpinning solid state TTA-UC.
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| 3. |
- Kamlar, Martin, 1981, et al.
(author)
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Polycyclizations of Ketoesters: Synthesis of Complex Tricycles with up to Five Stereogenic Centers from Available Starting Materials
- 2020
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In: Organic Letters. - : American Chemical Society (ACS). - 1523-7052 .- 1523-7060. ; 22:21, s. 8387-8391
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Journal article (peer-reviewed)abstract
- Here we present a polycyclization of oxotriphenylhexanoates. The polycyclization is governed by electronic effects, and three major synthetic paths have been established leading to stereochemically complex tricyclic frameworks with up to five stereogenic centers. The method is compatible with an array of functional groups, allowing pharmacophoric elements to be introduced post cyclization.
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| 4. |
- Kashinath Dhokale, Bhausaheb, 1985, et al.
(author)
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Microwave-heated γ-Alumina Applied to the Reduction of Aldehydes to Alcohols
- 2020
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In: ChemCatChem. - : Wiley. - 1867-3899 .- 1867-3880. ; 12:24, s. 6344-6355
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Journal article (peer-reviewed)abstract
- The development of cheap and robust heterogeneous catalysts for the Meerwein-Ponndorf-Verley (MPV) reduction is desirable due to the difficulties in product isolation and catalyst recovery associated with the traditional use of homogeneous catalysts for MPV. Herein, we show that microwave heated γ-Al2O3 can be used for the reduction of aldehydes to alcohols. The reaction is efficient and has a broad substrates scope (19 entries). The products can be isolated by simple filtration, and the catalyst can be regenerated. With the use of microwave heating, we can direct the heating to the catalyst rather than to the whole reaction medium. Furthermore, DFT was used to study the reaction mechanism, and we can conclude that a dual-site mechanism is operative where the aldehyde and 2-propoxide are situated on two adjacent Al sites during the reduction. Additionally, volcano plots were used to rationalize the reactivity of Al2O3 in comparison to other metal oxides.
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| 5. |
- Levin, Sune, 1991, et al.
(author)
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A nanofluidic device for parallel single nanoparticle catalysis in solution
- 2019
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 10:1
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Journal article (peer-reviewed)abstract
- Studying single catalyst nanoparticles, during reaction, eliminates averaging effects that are an inherent limitation of ensemble experiments. It enables establishing structure-function correlations beyond averaged properties by including particle-specific descriptors such as defects, chemical heterogeneity and microstructure. Driven by these prospects, several single particle catalysis concepts have been implemented. However, they all have limitations such as low throughput, or that they require very low reactant concentrations and/or reaction rates. In response, we present a nanofluidic device for highly parallelized single nanoparticle catalysis in solution, based on fluorescence microscopy. Our device enables parallel scrutiny of tens of single nanoparticles, each isolated inside its own nanofluidic channel, and at tunable reaction conditions, ranging from the fully mass transport limited regime to the surface reaction limited regime. In a wider perspective, our concept provides a versatile platform for highly parallelized single particle catalysis in solution and constitutes a promising application area for nanofluidics.
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| 6. |
- Runemark, August, 1993, et al.
(author)
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Aerobic Oxidative EDA Catalysis: Synthesis of Tetrahydroquinolines Using an Organocatalytic EDA Active Acceptor
- 2022
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In: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 87:2, s. 1457-1469
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Journal article (peer-reviewed)abstract
- A catalytic electron donor-acceptor (EDA) complex for the visible-light-driven annulation reaction between activated alkenes and N,N-substituted dialkyl anilines is reported. The key photoactive complex is formed in situ between dialkylated anilines as donors and 1,2-dibenzoylethylene as a catalytic acceptor. The catalytic acceptor is regenerated by aerobic oxidation. Investigations into the mechanism are provided, revealing a rare example of a catalytic acceptor in photoactive EDA complexes that can give access to selective functionalization of aromatic amines under mild photochemical conditions.
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| 7. |
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| 8. |
- Runemark, August, 1993, et al.
(author)
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Overcoming Back Electron Transfer in the Electron Donor-Acceptor Complex-Mediated Visible Light-Driven Generation of α-Aminoalkyl Radicals from Secondary Anilines
- 2023
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In: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 88:1, s. 462-474
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Journal article (peer-reviewed)abstract
- An additive-free, visible light-driven annulation between N-aryl amino acids and maleimide to form tetrahydroquinolines (THQs) is disclosed. Photochemical activation of an electron donor-acceptor (EDA) complex between amino acids and maleimides drives the reaction, and aerobic oxygen acts as the terminal oxidant in the net oxidative process. A range of N-aryl amino acids and maleimides have been investigated as substrates to furnish the target THQ in good to excellent yield. Mechanistic investigations, including titration and UV-vis studies, demonstrate the key role of the EDA complex as the photoactive species.
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| 9. |
- Runemark, August, 1993
(author)
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Photoactive EDA complexes in visible light driven aerobic oxidations
- 2022
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Doctoral thesis (other academic/artistic)abstract
- Organic synthesis driven by photochemical activation has been proven very promising in a range of scenarios within academia and industry. The emergence of photoredox catalysis has fueled an ever-growing interest in the use of visible light as a convenient energy source for a variety of radical reactions otherwise difficult to achieve. However, the use of homogeneous catalysts, based on transition metals or complicated organic dyes as the light harvesting moiety, does not come without drawbacks. Problems include the price and availability of ruthenium and iridium, and the separation and re-use of the catalysts from the products. Photochemical transformations that use simpler systems, such as catalyst-free versions or small organic molecules as photocatalysts, are therefore attractive to develop. For certain systems, one potential solution to these problems is the use of electron donor-acceptor (EDA) complexes. These complexes can form between a molecule of high electron affinity (acceptor) and a molecule of low ionization potential (donor). A key feature of the EDA complex is that it can be excited with light of a lower energy than that needed to excite the reactants on their own. The excitation of the complex can result in the formation of reactive radical species that can be harvested for further chemical reactions. EDA complexes can, with other words, be used as a convenient light-absorbing moiety to drive chemical reactions without the need of an external photocatalyst. Oxidation reactions are a universal part of organic chemistry. The oxidants commonly used are however associated with certain drawbacks such as troublesome waste production. Oxygen obtained from the air around us is a potentially ideal alternative. The use of aerobic conditions in the combination with photoactive EDA complexes poses an interesting and underdeveloped part of photochemical transformations. In this thesis, an EDA complex approach to the synthesis of N-heterocycles has been investigated. The developed methods use alkylated anilines as donors and activated alkenes as acceptors to form different EDA complexes. Visible light is used to activate the complexes, and aerobic oxygen is used as the terminal oxidant to furnish the target compounds. In the first part of the thesis, new EDA complexes between dialkyl anilines and 1,2-dibenzoyl ethylenes are identified. The results show that upon excitation of the EDA complexes, 3,4-disubstituted tetrahydroquinolines can be formed in excellent diastereoselectivity and in high yields. In the second part, the identified EDA complexes are used as part of a catalytic system for the generation of α-amino alkyl radicals under aerobic conditions and under visible light irradiation. Lastly, in the third part, new EDA complexes between arylated amino acids and maleimides are identified. The photoactivation of these complexes was shown to be an efficient way of generating secondary α-amino alkyl radicals to furnish N-H-tetrahydroquinolines.
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| 10. |
- Runemark, August, 1993, et al.
(author)
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Photochemical Access to Substituted β-Lactams and β-Lactones via the Zimmerman-O'Connell-Griffin Rearrangement
- 2023
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In: Organic Letters. - 1523-7052 .- 1523-7060. ; 25:29, s. 5520-5524
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Journal article (peer-reviewed)abstract
- A photomediated protocol giving facile access to substituted β-lactam and β-lactones is presented. The method realizes, for the first time, the use of the Zimmerman-O'Connell-Griffin (ZOG) rearrangement in [2 + 2] cycloaddition. Products are obtained in high yield with excellent diastereoselectivity under visible light irradiation and under mild reaction conditions.
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| 11. |
- Runemark, August, 1993, et al.
(author)
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Visible-Light-Driven Stereoselective Annulation of Alkyl Anilines and Dibenzoylethylenes via Electron Donor-Acceptor Complexes
- 2021
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In: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 86:2, s. 1901-1910
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Journal article (peer-reviewed)abstract
- A catalyst-free, stereoselective visible-light-driven annulation reaction between alkenes and N,N-substituted dialkyl anilines for the synthesis of substituted tetrahydroquinolines is presented. The reaction is driven by the photoexcitation of an electron donor-acceptor (EDA) complex, and the resulting products are obtained in good to high yields with complete diastereoselectivity. Mechanistic rationale and photochemical characterization of the EDA-complex are provided.
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