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Sökning: L773:0022 3263 > (2020-2024)

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1.
  • Adeyemi, Ahmed, et al. (författare)
  • Regio- and Stereoselective Synthesis of Allylic Spiroethers (Spirobenzofuranes) via an Intramolecular Mizoroki-Heck Reaction
  • 2020
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 85:12, s. 7648-7657
  • Tidskriftsartikel (refereegranskat)abstract
    • The palladium(0)-catalyzed intramolecular annulation of 12 1,3-disubstituted cyclopentenes, derived from (+)-vincelactam, resulted in 5-exo cyclizations which furnished a series of 2,5-dimethyl-14(3R,4'S)-2H-spiro[benzofuran-3,1'-cyclopentan]2'-en-4'-yl)-1H-pyrroles in excellent diastereoselectivities and useful isolated yields. The double bond migration process that followed the arylpalladium insertion was controlled by a fine-tuning of the reaction system, which provided regioselectivities of up to 98:2. The selective Mizoroki-Heck reaction was used as the key transformation for preparing two new spirocyclic monoprotected amino acids as single stereoisomers.
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2.
  • Adolfsson, Dan E., 1989-, et al. (författare)
  • Intramolecular Povarov Reactions for the Synthesis of Chromenopyridine fused 2-Pyridone Polyheterocycles Binding to α-Synuclein and Amyloid-β fibrils
  • 2020
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 85:21, s. 14174-14189
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • A BF3×OEt2 catalyzed intramolecular Povarov reaction was used to synthesize a library of 15 chromenopyridine fused thiazolino-2-pyridone peptidomimetics. The reaction works with a range of O-alkylated salicylaldehydes and amino functionalized thiazolino-2-pyridones, to generate polyheterocycles with diverse substitution. The synthesized compounds were screened for their ability to bind α-synuclein and amyloid β fibrils in vitro. Analogs substituted with a nitro group bind to mature amyloid fibrils, and the activity moreover depends on the positioning of this functional group.
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3.
  • Azzi, Emanuele, et al. (författare)
  • Visible Light Mediated Photocatalytic N‑Radical Cascade Reactivity of γ,δ-Unsaturated N‑Arylsulfonylhydrazones : A General Approach to Structurally Diverse Tetrahydropyridazines
  • 2021
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 86:4, s. 3300-3323
  • Tidskriftsartikel (refereegranskat)abstract
    • Tetrahydropyridazines are of particular interest for their versatility as intermediates in organic synthesis and display pharmacological activity in several domains. Here, we describe the photocatalytic synthesis of different tetrahydropyridazines starting from gamma,delta-unsaturated N-arylsulfonylhydrazones. Simple structural changes of substrates result into three different pathways beginning from a common N-hydrazonyl radical, which evolves through a domino carboamination/dearomatization, a HAT process, or a photoinduced radical Smiles rearrangement to afford diverse tetrahydropyridazines. All reactions are carried out in very mild conditions, and the quite inexpensive [Ru(bpy)(3)]Cl-2 is used as the catalyst. Preliminary mechanism studies are presented, among them luminescence and electrochemical characterization of the involved species. Computational studies allow to rationalize the mechanism in accord with the experimental findings.
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4.
  • Baumruck, A. C., et al. (författare)
  • Native Chemical Ligation of Highly Hydrophobic Peptides in Ionic Liquid-Containing Media
  • 2021
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 86:2, s. 1659-1666
  • Tidskriftsartikel (refereegranskat)abstract
    • The chemical synthesis of a highly hydrophobic membrane-associated peptide by native chemical ligation (NCL) in an ionic liquid (IL) [C2mim][OAc]/buffer mixture was achieved by employing peptide concentrations up to 11 mM. NCL was studied at different pH and water content and compared to several "gold-standard"ligation protocols. The optimized reaction protocol for the NCL in IL required the addition of 40% water and pH adjustment to 7.0-7.5, resulting in ligation yields of up to 80-95% within 1 to 4 h. This new ligation protocol is generally applicable and outperforms current "gold-standard"NCL methods. ©
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5.
  • Biosca, Maria, et al. (författare)
  • Mechanism of Asymmetric Homologation of Alkenylboronic Acids with CF3-Diazomethane via Borotropic Rearrangement
  • 2024
  • Ingår i: Journal of Organic Chemistry. - 0022-3263 .- 1520-6904. ; 89:7, s. 4538-4548
  • Tidskriftsartikel (refereegranskat)abstract
    • Density functional theory calculations have been performed to investigate the mechanism for the BINOL-catalyzed asymmetric homologation of alkenylboronic acids with CF3-diazomethane. The reaction proceeds via a chiral BINOL ester of the alkenylboronic acid substrate. The calculations reveal a complex scenario for the formation of the chiral BINOL-alkenylboronate species, which is the key intermediate in the catalytic process. The aliphatic alcohol additive plays an important role in the reaction. This study provides a rationalization of the stereoinduction step of the reaction, and the enantioselectivity is mainly attributed to the steric repulsion between the CF3 group of the diazomethane reagent and the γ-substituent of the BINOL catalyst. The complex potential energy surface obtained by the calculations is analyzed by means of microkinetic simulations.
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6.
  • Brea, Oriana, et al. (författare)
  • Mechanisms of Formation and Rearrangement of Benziodoxole-Based CF3 and SCF3 Transfer Reagents
  • 2020
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 85:23, s. 15577-15585
  • Tidskriftsartikel (refereegranskat)abstract
    • Togni's benziodoxole-based reagents are widely used in trifluoromethylation reactions. It has been established that the kinetically stable hypervalent iodine form (I-CF3) of the reagents is thermodynamically less stable than its acyclic ether isomer (O-CF3). On the other hand, the trifluoromethylthio analogue exists in the thermodynamically stable thioperoxide form (O-SCF3), and the hypervalent form (I-SCF3) has been elusive. Despite the importance of these reagents, very little is known about the reaction mechanisms of their syntheses, which has hampered the development of new reagents of the same family. Herein, we use density functional theory calculations to understand the reasons for the divergent behaviors between the CF3 and SCF3 reagents. We demonstrate that they follow different mechanisms of formation and that the metals involved in the syntheses (potassium in the case of the trifluoromethyl reagent and silver in the trifluoromethylthio analogue) play key roles in the mechanisms and greatly influence the possibility of their rearrangements from the hypervalent (I-CF3, I-SCF3) to the corresponding ether-type form (O-CF3, O-SCF3).
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7.
  • Burke, Anthony, et al. (författare)
  • Recent Advances in Asymmetric Hydrogenation Catalysis Utilizing Spiro and Other Rigid C-Stereogenic Phosphine Ligands
  • 2022
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society. - 0022-3263 .- 1520-6904. ; 87:4, s. 1898-1924
  • Tidskriftsartikel (refereegranskat)abstract
    • Transition-metal-catalyzed asymmetric reactions have been a powerful tool in organic synthesis for many years. The design of chiral ligands with the right configuration is fundamental to induce high regio- and stereoselectivity to catalytic reactions and to achieve high turnover numbers and high yields. A challenge is the control of prochiral centers with similar electronic properties in a similar steric environment within the same molecule. Over the last 10 years, a range of novel rigid C-stereogenic chiral phosphine ligands has been developed and successfully applied in various types of asymmetric transformations. Many of these ligands are of a di-, tri-, or multidentate nature. The purpose of this Perspective is to highlight recent synthetic achievements (since 2010) with spiro-phosphines and other rigid phosphines and discuss some mechanistic aspects of the catalytic reactions. 
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8.
  • Cao, Guanyue, et al. (författare)
  • Porphyrindiene-Based Tandem Diels-Alder Reaction for Preparing Low-Symmetry pi-Extended Porphyrins with Push-Pull Skeletons
  • 2022
  • Ingår i: Journal of Organic Chemistry. - : AMER CHEMICAL SOC. - 0022-3263 .- 1520-6904. ; 87:14, s. 9001-9010
  • Tidskriftsartikel (refereegranskat)abstract
    • Tandem Diels-Alder reactions of masked porphyrindienes (i.e., sulfolenoporphyrins) with benzoquinones and stilbenes, followed by aromatization, have been developed to load porphyrin with mixed annulation units (i.e., terphenyl and naphthoquinone), furnishing the low-symmetry pi-extended porphyrins (DxAy) with push-pull skeletons. All low-symmetrical chromophores display panchromatic absorption spectra, which look like a spectral combination of symmetrical congeners (D4/A4) in a certain ratio. Among them, tD2A2 with trans-arrangement of push/pull units possesses the largest maximum centered at 766 nm with the onset around 900 nm. The fusion of the electron-deficient naphthoquinone moiety on the porphyrin core results in the approximately quantitative regulation of the E-ox1 and HOMOs (i.e., 0.10-0.13 V increase for the E-ox1 and 0.14-0.16 eV decrease for the HOMOs per naphthoquinone unit). In brief, this work provides a new way to construct low-symmetry pi-extended porphyrins with tunable properties resorting to the ratios and locations of the annulated push-pull units.
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9.
  • Carreiro, Elisabete P., et al. (författare)
  • Asymmetric Additions Empowered by OrganoCatalysts, Metal Catalysts, and Deep Natural Eutectic Solvents (NADES)
  • 2024
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society. - 0022-3263 .- 1520-6904. ; 89, s. 6631-
  • Tidskriftsartikel (refereegranskat)abstract
    • This article is a history of an industrial-academic partnership that started almost two decades ago and details the evolution of a relationship between a small academic research group and a spin-out company located in Portugal. Their activities have ranged from the development of new metal-based catalytic systems for asymmetric epoxidations, allylic alkylations, and arylations to the development of novel cinchona-based organocatalysts for asymmetric hydrosilylations and Michael additions. Current common interests are centered on the development of novel chiral Natural Deep Eutectic Solvent systems, which they are investigating in different types of reaction systems.
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10.
  • Dunås, Petter, 1990, et al. (författare)
  • Azulene functionalization by iron-mediated addition to a cyclohexadiene scaffold
  • 2020
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 85:21, s. 13453-16465
  • Tidskriftsartikel (refereegranskat)abstract
    • The functionalization of azulenes via reaction with cationic η5-iron carbonyl diene complexes under mild reaction conditions is demonstrated. A range of azulenes, including derivatives of naturally occurring guaiazulene, were investigated in reactions with three electrophilic iron complexes of varying electronic properties, affording the desired coupling products in 43−98% yield. The products were examined with UV− vis/fluorescence spectroscopy and showed interesting halochromic properties. Decomplexation and further derivatization of the products provide access to several different classes of 1-substituted azulenes, including a conjugated ketone and a fused tetracycle.
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11.
  • Ekebergh, Andreas, 1984, et al. (författare)
  • Ruthenium-Catalyzed E-Selective Alkyne Semihydrogenation with Alcohols as Hydrogen Donors
  • 2020
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 85:5, s. 2966-2975
  • Tidskriftsartikel (refereegranskat)abstract
    • Selective direct ruthenium-catalyzed semihydrogenation of diaryl alkynes to the corresponding E-alkenes has been achieved using alcohols as the hydrogen source. The method employs a simple ruthenium catalyst, does not require external ligands, and affords the desired products in > 99% NMR yield in most cases (up to 93% isolated yield). Best results were obtained using benzyl alcohol as the hydrogen donor, although biorenewable alcohols such as furfuryl alcohol could also be applied. In addition, tandem semihydrogenation-alkylation reactions were demonstrated, with potential applications in the synthesis of resveratrol derivatives.
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12.
  • Escobar, Zilma, et al. (författare)
  • Stereoretentive Nucleophilic Substitution at the Tetrasubstituted Carbon of Galiellalactone
  • 2020
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 85:12, s. 7704-7710
  • Tidskriftsartikel (refereegranskat)abstract
    • The fungal metabolite galiellalactone (1) was, as its acetate 4, discovered to undergo a substitution reaction with cysteine derivatives. By studying the reaction mechanism and the intermediates formed, and in an effort to expand the chemical diversity of the galiellalactonoids, a mild and general method of preparing ether, thioether, and amine analogues of galiellalactone was developed. The reaction is a formal stereoretentive nucleophilic substitution at an oxygenated tertiary carbon. NMR analysis of the progressing reaction shows that it involves an initial allylic substitution to form a new Michael acceptor, followed by the addition of a second equivalent of the nucleophile to this and, finally, a retro Michael reaction. This restores the original galiellalactone system with a double bond between C-2a and C-3, but with a new substituent at C-7b. As galiellalactone is a promising STAT3 inhibitor, this novel transformation facilitates the semisynthesis of a wide variety of new analogues for structure-activity relationship studies.
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13.
  • Geng, Xin, et al. (författare)
  • Construction of Phenanthridinone Skeletons through Palladium-Catalyzed Annulation
  • 2023
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 88:17, s. 12738-12743
  • Tidskriftsartikel (refereegranskat)abstract
    • Herein, a straightforward synthetic approach for the construction of phenanthridin-6(5H)-one skeletons is disclosed. The developed protocol relies on palladium catalysis, providing controlled access to a range of functionalized phenanthridin-6(5H)-ones in 59-88% yields. Furthermore, plausible reaction pathways are proposed based on mechanistic experiments.
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14.
  • Green, Joshua P., et al. (författare)
  • Golden Age of Fluorenylidene Phosphaalkenes-Synthesis, Structures, and Optical Properties of Heteroaromatic Derivatives and Their Gold Complexes
  • 2020
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 85:22, s. 14619-14626
  • Tidskriftsartikel (refereegranskat)abstract
    • The substitution of 2,7-dibromo-9-fluorenyl phosphaalkenes with heteroaromatic substituents (bithiophene, benzothiophene, pyridine) offers access to interesting push-pull dye molecules. Steric shielding due to the bulky P-substituent gives marked different reactivities at the 2- and 7-positions, allowing the synthesis of mixed/asymmetric derivatives. Further functionalization via gold(I) coordination was demonstrated and increased the acceptor character, concomitant with a red-shifted absorption.
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15.
  • Jiang, Xingguo, et al. (författare)
  • Trifluoromethylthiolation, Trifluoromethylation, and Arylation Reactions of Difluoro Enol Silyl Ethers
  • 2020
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 85:13, s. 8311-8319
  • Tidskriftsartikel (refereegranskat)abstract
    • This study reports a new application area of difluoro enol silyl ethers, which can be easily obtained from trifluoromethyl ketones. The main focus has been directed to the electrophilic fluoroalkylation and arylation methods. The trifluoromethylthiolation of difluoro enol silyl ethers can be used for the construction of a novel trifluoromethylthio-alpha, alpha-difluoroketone (-COCF2SCF3) functionality. The -CF2SCF3 moiety has interesting properties due to the electron-withdrawing, albeit lipophilic, character of the SCF3 group, which can be combined with the high electrophilicity of the difluoroketone motif. The methodology could also be extended to difluoro homologation of the trifluoromethyl ketones using the Togni reagent. In addition, we presented a method for transition-metal-free arylation of difluoro enol silyl ethers based on hypervalent iodines.
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16.
  • Johansson, Emil, et al. (författare)
  • Synthesis of 4-O-alkylated N-acetylneuraminic acid derivatives
  • 2021
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 86:13, s. 9145-9154
  • Tidskriftsartikel (refereegranskat)abstract
    • The synthesis of 4-O-alkyl analogs of N-acetylneuraminic acid (Neu5Ac) and the scope of the reaction are described. Activated alkyl halides and sulfonates and primary alkyl iodides give products in useful yields. The utility of the methodology is exemplified using a thiophenyl Neu5Ac building block to synthesize a 4-O-alkyl DANA analog. These results expand the toolbox of Neu5Ac chemistry with value in drug discovery and for the design of novel tools to study the biology of Neu5Ac lectins. 
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17.
  • Kagho, Mervic D., et al. (författare)
  • Total Synthesis via Biomimetic Late-Stage Heterocyclization: Assignment of the Relative Configuration and Biological Evaluation of the Nitraria Alkaloid (±)-Nitrabirine
  • 2021
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 86, s. 14903-14914
  • Tidskriftsartikel (refereegranskat)abstract
    • The racemic total synthesis of nitrabirine (5) together with its previously undescribed epimer 2-epi nitrabirine (5′) is accomplished via a six-step route based on a biomimetic late-stage heterocyclization. This allowed the assignment of the relative configuration of nitrabirine by the lanthanide-induced shifts (LIS) experiment, which was later on confirmed by X-ray diffraction of obtained single crystals. Furthermore, oxidation studies demonstrated that the direct N-oxidation of nitrabirine does not yield nitrabirine N-oxide as reported earlier. In contrast, the reaction of hydrogen peroxide with nitrabirine (5) yields the salt 24′, whereas 2-epi nitrabirine (5′) surprisingly leads to a previously uncharacterized product 22 under the same conditions. Finally, a Fischer indole reaction gave access to novel tetracyclic nitrabirine derivatives 26a-d. A comprehensive biological evaluation of nitrabirine (5), 2-epi nitrabirine (5′), and all derivatives synthesized in this study revealed general biofilm dispersal effects against Candida albicans. Moreover, specific compounds showed moderate antibacterial activities as well as potent cytotoxic activities.
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18.
  • Kalapos, Peter Pal, et al. (författare)
  • Photoswitching of Local (Anti)Aromaticity in Biphenylene-Based Diarylethene Molecular Switches
  • 2022
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 87:15, s. 9532-9542
  • Tidskriftsartikel (refereegranskat)abstract
    • Photoinduced tuning of (anti)aromaticity and associated molecular properties is currently in the focus of attention for both tailoring photochemical reactivity and designing new materials. Here, we report on the synthesis and spectroscopic characterization of diarylethene-based molecular switches embedded in a biphenylene structure composed of rings with different levels of local (anti)aromaticity. We show that it is possible to modulate and control the (anti)aromatic character of each ring through reversible photoswitching of the aryl units of the system between open and closed forms. Remarkably, it is shown that the irreversible formation of an annulated bis(dihydro-thiopyran) side-product that hampers the photoswitching can be efficiently suppressed when the aryl core formed by thienyl groups in one switch is replaced by thiazolyl groups in another.
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19.
  • Kalapos, Peter Pal, et al. (författare)
  • Salicylideneaniline/Dithienylethene Hybrid Molecular Switches: Design, Synthesis, and Photochromism
  • 2023
  • Ingår i: Journal of Organic Chemistry. - : AMER CHEMICAL SOC. - 0022-3263 .- 1520-6904. ; 89:1, s. 16-26
  • Tidskriftsartikel (refereegranskat)abstract
    • A hybrid molecular switch comprising salicylideneaniline (SA) and dithienylethene (DTE) moieties around a single benzene ring is reported. Due to an interplay between solvent-assisted enol-keto tautomerization in the former moiety and photochromic electrocyclization in the latter, this dithienylbenzene derivative was found to be photoresponsive at room temperature with a thermally stable closed form. The main photoproduct featuring ring-closed DTE and keto-enamine SA structures could be isolated and converted back to the starting material by irradiation with visible light. The optical properties of the potential structures involved in the overall process were characterized by using density functional theory (DFT) calculations in good agreement with the measured data. The reversibility of the conversion could be tuned by the presence of donor and acceptor substituents, while the introduction of the imine in the form of a benzothiazole moiety enabled photochemistry even in nonprotic solvents.
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20.
  • Kamlar, Martin, 1981, et al. (författare)
  • Synthesis of cis-Oriented Vicinal Diphenylethylenes through a Lewis Acid-Promoted Annulation of Oxotriphenylhexanoates
  • 2021
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 86:13, s. 8660-8671
  • Tidskriftsartikel (refereegranskat)abstract
    • This study explores the synthesis of cyclic cis-vicinal phenyl ethylenes from oxotriphenylhexanoates. The reaction is a BBr3-promoted cyclization of 1,6-ketoesters (1) to five-membered diketo compounds (2). The synthesis is interesting as it constitutes one of the few examples of modular stereoselective synthesis of structures with a cis-oriented vicinal diphenylethylene. The core structure of 2 can be smoothly derivatized, which makes it a promising synthetic building block for further stereoselective synthetic applications.
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21.
  • Kunz, Susanna, et al. (författare)
  • Derivatization of 2,1,3-Benzothiadiazole via Regioselective C–H Functionalization and Aryne Reactivity
  • 2024
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 89:9, s. 6138-6148
  • Tidskriftsartikel (refereegranskat)abstract
    • Despite growing interest in 2,1,3-benzothiadiazole (BTD) as an integral component of many functional molecules, methods for the functionalization of its benzenoid ring have remained limited, and many even simply decorated BTDs have required de novo synthesis. We show that regioselective Ir-catalyzed C–H borylation allows access to versatile 5-boryl or 4,6-diboryl BTD building blocks, which undergo functionalization at the C4, C5, C6, and C7 positions. The optimization and regioselectivity of C–H borylation are discussed. A broad reaction scope is presented, encompassing ipso substitution at the C–B bond, the first examples of ortho-directed C–H functionalization of BTD, ring closing reactions to generate fused ring systems, as well as the generation and capture reactions of novel BTD-based heteroarynes. The regioselectivity of the latter is discussed with reference to the Aryne Distortion Model.
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22.
  • Lindman, Jens, 1990-, et al. (författare)
  • Two-chamber Aminocarbonylation of Aryl Bromides and Triflates Using Amino Acids as Nucleophiles
  • 2023
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 88:18, s. 12978-12985
  • Tidskriftsartikel (refereegranskat)abstract
    • A palladium(0)-catalyzed aminocarbonylation reaction employing molybdenum hexacarbonyl as a carbon monoxide precursor for the production of N-capped amino acids using aryl and heteroaryl bromides and triflates is reported. The carbon monoxide is formed ex situ through the use of a two-chamber system, where carbon monoxide generated in one chamber is free to diffuse over and be consumed in the other palladium-catalyzed reaction chamber. Using this method, two series of aryl bromides and aryl triflates were utilized to synthesize 21 N-capped amino acids in isolated yields between 40 and 91%.
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23.
  • Mayer, Peter J., et al. (författare)
  • Structure–Property Relationships in Unsymmetric Bis(antiaromatics) : Who Wins the Battle between Pentalene and Benzocyclobutadiene?
  • 2020
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 85:8, s. 5158-5172
  • Tidskriftsartikel (refereegranskat)abstract
    • According to the currently accepted structure-property relationships, aceno-pentalenes with an angular shape (fused to the 1,2-bond of the acene) exhibit higher antiaromaticity than those with a linear shape (fused to the 2,3-bond of the acene). To explore and expand the current view, we designed and synthesized molecules where two isomeric, yet, different, 8 pi antiaromatic subunits, a benzocyclobutadiene (BCB) and a pentalene, are combined into, respectively, an angular and a linear topology via an unsaturated six-membered ring. The antiaromatic character of the molecules is supported experimentally by H-1 NMR, UV-vis, and cyclic voltammetry measurements and X-ray crystallography. The experimental results are further confirmed by theoretical studies including the calculation of several aromaticity indices (NICS, ACID, HOMA, FLU, MCI). In the case of the angular molecule, double bond-localization within the connecting six-membered ring resulted in reduced antiaromaticity of both the BCB and pentalene subunits, while the linear structure provided a competitive situation for the two unequal [4n]pi subunits. We found that in the latter case the BCB unit alleviated its unfavorable antiaromaticity more efficiently, leaving the pentalene with strong antiaromaticity. Thus, a reversed structure-antiaromaticity relationship when compared to aceno-pentalenes was achieved.
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24.
  • Mkrtchyan, Satenik, et al. (författare)
  • Mechanochemical Defluorinative Arylation of Trifluoroacetamides : An Entry to Aromatic Amides
  • 2023
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 88:2, s. 863-870
  • Tidskriftsartikel (refereegranskat)abstract
    • The amide bond is prominent in natural and synthetic organic molecules endowed with activity in various fields. Among a wide array of amide synthetic methods, substitution on a pre-existing (O)C-N moiety is an underexplored strategy for the synthesis of amides. In this work, we disclose a new protocol for the defluorinative arylation of aliphatic and aromatic trifluoroacetamides yielding aromatic amides. The mechanochemically induced reaction of either arylboronic acids, trimethoxyphenylsilanes, diaryliodonium salts, or dimethyl(phenyl)sulfonium salts with trifluoroacetamides affords substituted aromatic amides in good to excellent yields. These nickel-catalyzed reactions are enabled by C-CF3 bond activation using Dy2O3 as an additive. The current protocol provides versatile and scalable routes for accessing a wide variety of substituted aromatic amides. Moreover, the protocol described in this work overcomes the drawbacks and limitations in the previously reported methods.
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25.
  • Naidu, Veluru Ramesh, et al. (författare)
  • Synthesis of Cross-Conjugated Polyenes via Palladium-Catalyzed Oxidative C-C Bond Forming Cascade Reactions of Allenes
  • 2020
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 85:8, s. 5428-5437
  • Tidskriftsartikel (refereegranskat)abstract
    • An efficient palladium-catalyzed oxidative C-C bond forming cascade reaction of allenes involving a coupling between an enallene and an allenyne followed by a carbocyclization of the generated Pd-intermediate was developed. This cascade reaction afforded functionalized cross-conjugated polyenes. The enallene is initially activated by palladium and reacts with the allenyne to give the cross-conjugated polyenes.
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26.
  • Oruganti, Baswanth, et al. (författare)
  • Modulating the Photocyclization Reactivity of Diarylethenes through Changes in the Excited-State Aromaticity of the it-Linker
  • 2022
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 87:17, s. 11565-11571
  • Tidskriftsartikel (refereegranskat)abstract
    • Quantum chemical calculations are performed to explore if the reactivity of diarylethene switches toward photocyclization can be controlled by the excited-state aromaticity of their bridging pi-linker. Using an archetypal diarylethene with a non aromatic pi-linker as a reference, completely different outcomes are found when the pi-linker is allowed to become either aromatic (no reaction) or antiaromatic (fast reaction) upon photoexcitation. The results demonstrate a possibility to use the excited-state aromaticity concept for actual modulation of photochemical reactivity.
  •  
27.
  • Pourghasemi Lati, Monireh, et al. (författare)
  • A Study of an 8-Aminoquinoline-Directed C(sp2)–H Arylation Reaction on the Route to Chiral Cyclobutane Keto Acids from Myrtenal
  • 2021
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 86:12, s. 8527-8537
  • Tidskriftsartikel (refereegranskat)abstract
    • This work outlines a synthetic route that can be used to access chiral cyclobutane keto acids with two stereocenters in five steps from the inexpensive terpene myrtenal. Furthermore, the developed route includes an 8-aminoquinoline-directed C(sp2)–H arylation as one of its key steps, which allows a wide range of aryl and heteroaryl groups to be incorporated into the bicyclic myrtenal scaffold prior to the ozonolysis-based ring-opening step that furnishes the target cyclobutane keto acids. This synthetic route is expected to find many applications connected to the synthesis of natural product-like compounds and small molecule libraries.
  •  
28.
  • Proietti, Giampiero, et al. (författare)
  • Accessing Perfluoroaryl Sulfonimidamides and Sulfoximines via Photogenerated Perfluoroaryl Nitrenes : Synthesis and Application as a Chiral Auxiliary
  • 2021
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 86:23, s. 17119-17128
  • Tidskriftsartikel (refereegranskat)abstract
    • Sulfonimidamides (SIAs) and sulfoximines (SOIs) have attracted attention due to their potential in agriculture and in medicinal chemistry as bioisosteres of biologically active compounds, and new synthetic methods are needed to access and explore these compounds. Herein, we present a light-promoted generation of perfluorinated aromatic nitrenes, from perfluorinated azides, that subsequently are allowed to react with sulfinamides and sulfoxides, generating achiral and chiral SIAs and SOIs. One of the enantiopure SIAs was evaluated as a novel chiral auxiliary in Grignard additions to the imines yielding the product in up to 96:4 diastereomeric ratio.
  •  
29.
  • Qi, Yunchuan, et al. (författare)
  • Spontaneous and Selective Macrocyclization in Nitroaldol Reaction Systems
  • 2023
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 89:2, s. 1091-1098
  • Tidskriftsartikel (refereegranskat)abstract
    • Through a dynamic polymerization and self-sorting process, a range of lowellane macrocycles have been efficiently generated in nitroaldol systems composed of aromatic dialdehydes and aliphatic or aromatic dinitroalkanes. All identified macrocycles show a composition of two repeating units, resulting in tetra-beta-nitroalcohols of different structures. The effects of the building block structure on the macrocyclization process have been demonstrated, and the influence from the solvent has been explored. In general, the formation of the lowellanes was amplified in response to phase-change effects, although solution-phase structures were, in some cases, favored.
  •  
30.
  • Reutskaya, Elena, et al. (författare)
  • Sulfur Oxidation Increases the Rate of HIRE-Type [1.4]Thiazepinone Ring Expansion and Influences the Conformation of a Medium-Sized Heterocyclic Scaffold
  • 2021
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 86:8, s. 5778-5791
  • Tidskriftsartikel (refereegranskat)abstract
    • The hydrated imidazoline ring expansion (HIRE-type) reaction was investigated for a series of di(hetero)arene-fused [1.4]thiazepinones in comparison with their sulfone counterparts. The sulfones were found to undergo ring expansion at a much higher rate compared to the thioethers, much in line with the current mechanistic understanding of the process. Moreover, the amide bond cis- and trans-isomers of the ring-expanded products were found, in the case of sulfones, to be stabilized through an intramolecular hydrogen bond. The latter phenomenon was studied in detail by NMR experiments and corroborated by X-ray crystallographic information.
  •  
31.
  • Runemark, August, 1993, et al. (författare)
  • Aerobic Oxidative EDA Catalysis: Synthesis of Tetrahydroquinolines Using an Organocatalytic EDA Active Acceptor
  • 2022
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 87:2, s. 1457-1469
  • Tidskriftsartikel (refereegranskat)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.
  •  
32.
  • Runemark, August, 1993, et al. (författare)
  • Overcoming Back Electron Transfer in the Electron Donor-Acceptor Complex-Mediated Visible Light-Driven Generation of α-Aminoalkyl Radicals from Secondary Anilines
  • 2023
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 88:1, s. 462-474
  • Tidskriftsartikel (refereegranskat)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.
  •  
33.
  • Runemark, August, 1993, et al. (författare)
  • Visible-Light-Driven Stereoselective Annulation of Alkyl Anilines and Dibenzoylethylenes via Electron Donor-Acceptor Complexes
  • 2021
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 86:2, s. 1901-1910
  • Tidskriftsartikel (refereegranskat)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.
  •  
34.
  • Rydfjord, Jonas, et al. (författare)
  • Acyl Amidines by Pd-Catalyzed Aminocarbonylation : One-Pot Cyclizations and C-11 Labeling
  • 2023
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 88:8, s. 5078-5089
  • Tidskriftsartikel (refereegranskat)abstract
    • A protocol for the carbonylative synthesis of acyl amidines from aryl halides, amidines, and carbon monoxide catalyzed by Pd(0) is reported herein. Notably, carbon monoxide is generated ex situ from a solid CO source, and several productive palladium ligands were identified with complementary benefits and substrate scope. Furthermore, sequential one-pot, two-step protocols for the synthesis of 1,2,4-triazoles and 1,2,4-oxadiazoles via acyl amidine intermediates are reported. In addition, this approach was extended to isotopic labeling using [11C]carbon monoxide to allow, for the first time, synthesis of 11C-labeled acyl amidines as well as a 11C-labeled 1,2,4-oxadiazole.
  •  
35.
  • Rydfjord, Jonas, et al. (författare)
  • Palladium-Mediated Synthesis of [Carbonyl-11C]acyl Amidines from Aryl Iodides and Aryl Bromides and Their One-Pot Cyclization to 11C-Labeled Oxadiazoles
  • 2022
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 88:8, s. 5118-5126
  • Tidskriftsartikel (refereegranskat)abstract
    • Positron emission tomography (PET) is a highly valuable imaging technique with many clinical applications. The possibility to study physiological and biochemical processes in vivo also makes PET an important tool in drug discovery. Of importance is the possibility of labelling the compound of interest with a positron-emitting radionuclide, such as carbon-11. Carbonylation reactions with [11C]carbon monoxide ([11C]CO) has been used to label a number of molecules containing a carbonyl derivative, such as amides and esters, with carbon-11. Presented herein is the palladium-mediated carbonylative synthesis of [carbonyl-11C]acyl amidines and their subsequent cyclization to 11C labeled 1,2,4-oxadiazoles. Starting from amidines, [11C]CO, and either aryl iodides or aryl bromides, [carbonyl-11C]acyl amidines were synthesized and isolated in good to very good radiochemical yields (RCY). The 11C-labeled 1,2,4-oxadiazoles were synthesized without the isolation of the intermediate [carbonyl-11C]acyl amidines and isolated in useful RCYs, including the NF-E2-related factor 2 activator DDO-7263. 3-Phenyl-5-(4-tolyl)-1,2,4-(5-11C)oxadiazole was synthesized and isolated with a clinically relevant molar activity. The broadened substrate scope, together with the good RCY and high Am, demonstrates the utility of this method for the incorporation of carbon-11 into acyl amidines and 1,2,4-oxadiazoles, structural motifs of pharmacological interest.
  •  
36.
  • Santoro, Stefano, et al. (författare)
  • Mechanism of the Kinugasa Reaction Revisited
  • 2021
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 86:15, s. 10665-10671
  • Tidskriftsartikel (refereegranskat)abstract
    • The mechanism of the Kinugasa reaction, that is, the copper-catalyzed formation of beta-lactams from nitrones and terminal alkynes, is re-evaluated by means of density functional theory calculations and in light of recent experimental findings. Different possible mechanistic scenarios are investigated using phenanthroline as a ligand and triethylamine as a base. The calculations confirm that after an initial two-step cycloaddition promoted by two copper ions, the resulting five-membered ring intermediate can undergo a fast and irreversible cycloreversion to generate an imine and a dicopper-ketenyl intermediate. From there, the reaction can proceed through a nucleophilic attack of a ketenyl copper intermediate on the imine and an intramolecular cyclization, rather than through the previously suggested (2 + 2) Staudinger synthesis.
  •  
37.
  •  
38.
  • Schepper, Jonas D. W., et al. (författare)
  • Preparation of Structurally and Electronically Diverse N -> B-Ladder Boranes by [2+2+2] Cycloaddition
  • 2021
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 86:21, s. 14767-14776
  • Tidskriftsartikel (refereegranskat)abstract
    • We report the synthesis of a series of eight N -> B-ladder boranes through cobalt-mediated cyclotrimerization of (2-cyanophenyl)-dimesitylborane with different dialkynes. The resulting tetracoordinate boranes show variable electrochemical and optical properties depending on the substitution pattern in the backbone of the coordinating pyridine-derivatives. While boranes containing alkyl-substituted pyridines show lower electron affinities than the known parent compound, boranes featuring pi-extended pyridine derivatives show higher electron affinities in the range of acceptor substituted triarylboranes. All derivatives show larger Stokes shifts (8790-6920 cm(-1)) compared to the N -> B-ladder borane coordinated by an unsubstituted pyridine.
  •  
39.
  • Schäfer, Clara, 1992, et al. (författare)
  • Effect of the Aza-N-Bridge and Push-Pull Moieties: A Comparative Study between BODIPYs and Aza-BODIPYs
  • 2022
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 87:5, s. 2569-2579
  • Tidskriftsartikel (refereegranskat)abstract
    • In the field of fluorescent dyes, difluoroboron-dipyrromethenes (BODIPY) have a highly respected position. To predict their photophysical properties prior to synthesis and therefore to successfully design molecules specifically for one’s needs, a solid structure-function understanding based on experimental observations is vital. This work delivers a photophysical evaluation of BODIPY and aza-BODIPY derivatives equipped with different electron-withdrawing/-donating substituents. Using combinatorial chemistry, pyrroles substituted with electron-donating/-withdrawing substituents were condensed together in two different manners, thus providing two sets of molecules. The only difference between the two sets is the bridging unit providing a so far lacking comparison between BODIPYs and aza-BODIPYs structural homologues. Replacing the meso-methine bridge with an aza-N bridge results in a red-shifted transition and considerably different, temperature-activated, excited-state relaxation pathways. The effect of electron-donating units on the absorption but not emission for BODIPYs was suppressed compared to aza-BODIPYs. This result could be evident in a substitution pattern-dependent Stokes shift. The outlook of this study is a deeper understanding of the structure-optics relationship of the (aza)-BODIPY-dye class, leading to an improvement in the de novo design of tailor-made molecules for future applications. © 2022 The Authors. Published by American Chemical Society
  •  
40.
  • Shen, Xuanyu, et al. (författare)
  • Silver-Assisted [3+2] Annulation of Nitrones with Isocyanides : Synthesis of 2,3,4-Trisubstituted 1,2,4-Oxadiazolidin-5-ones
  • 2020
  • Ingår i: Journal of Organic Chemistry. - : AMER CHEMICAL SOC. - 0022-3263 .- 1520-6904. ; 85:5, s. 3560-3567
  • Tidskriftsartikel (refereegranskat)abstract
    • A silver-assisted method for [3 + 2] annulation of nitrones with isocyanides has been developed. The developed protocol allows access to a variety of 2,3,4-trisubstituted 1,2,4-oxadiazolidin-S-one derivatives as single diastereomers in good to excellent yields using silver oxide as the catalyst and molecular oxygen as the terminal oxidant. A plausible mechanism involving a nucleophilic addition/cyclization/protodeargentation/oxidation pathway is proposed on the basis of experimental results.
  •  
41.
  • Szeler, Klaudia, et al. (författare)
  • Modeling the Alkaline Hydrolysis of Diaryl Sulfate Diesters : A Mechanistic Study
  • 2020
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 85:10, s. 6489-6497
  • Tidskriftsartikel (refereegranskat)abstract
    • Phosphate and sulfate esters have important roles in regulating cellular processes. However, while there has been substantial experimental and computational investigation of the mechanisms and the transition states involved in phosphate ester hydrolysis, there is far less work on sulfate ester hydrolysis. Here, we report a detailed computational study of the alkaline hydrolysis of diary! sulfate diesters, using different DFT functionals as well as mixed implicit/explicit solvation with varying numbers of explicit water molecules. We consider the impact of the computational model on computed linear free-energy relationships (LFER) and the nature of the transition states (TS) involved. We obtain good qualitative agreement with experimental LFER data when using a pure implicit solvent model and excellent agreement with experimental kinetic isotope effects for all models used. Our calculations suggest that sulfate diester hydrolysis proceeds through loose transition states, with minimal bond formation to the nucleophile and bond cleavage to the leaving group already initiated. Comparison to prior work indicates that these TS are similar in nature to those for the alkaline hydrolysis of neutral arylsulfonate monoesters or charged phosphate diesters and fluorophosphates. Obtaining more detailed insights into the transition states involved assists in understanding the selectivity of enzymes that hydrolyze these reactions.
  •  
42.
  • Tasić, Magdalena, et al. (författare)
  • Copper(I) Catalyzed Decarboxylative Synthesis of Diareno[ a, e]cyclooctatetraenes
  • 2022
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 87:11, s. 7501-7508
  • Tidskriftsartikel (refereegranskat)abstract
    • Diareno[a,e]cyclooctatetraenes find widespread applications as building blocks, ligands, and responsive cores in topologically switchable materials. However, current synthetic methods to these structures suffer from low yields or operational disadvantages. Here, we describe a practical three-step approach to diareno[a,e]cyclooctatetraenes using an efficient copper(I) catalyzed double decarboxylation as the key step. The sequence relies on cheap and abundant reagents, is readily performed on scale, and is amenable also to unsymmetrical derivatives that expand the utility of this intriguing class of structures.
  •  
43.
  • Tyagi, Mohit, et al. (författare)
  • Tandem Ring Opening/Intramolecular [2 + 2] Cycloaddition Reaction for the Synthesis of Cyclobutane Fused Thiazolino-2-Pyridones
  • 2021
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 86:23, s. 16582-16592
  • Tidskriftsartikel (refereegranskat)abstract
    • Reaction of thiazoline fused 2-pyridones with alkyl halides in the presence of cesium carbonate opens the thiazoline ring via S-alkylation and generates N-alkenyl functionalized 2-pyridones. In the reaction with propargyl bromide, the thiazoline ring opens and subsequently closes via a [2 + 2] cycloaddition between an in situ generated allene and the α,β-unsaturated methyl ester. This method enabled the synthesis of a variety of cyclobutane fused thiazolino-2-pyridones, of which a few analogues inhibit amyloid β1–40 fibril formation. Furthermore, other analogues were able to bind mature α-synuclein and amyloid β1−40 fibrils. Several thiazoline fused 2-pyridones with biological activity tolerate this transformation, which in addition provides an exocyclic alkene as a potential handle for tuning bioactivity.
  •  
44.
  • Villo, Piret, et al. (författare)
  • Kinetic Analysis as an Optimization Tool for Catalytic Esterification with a Moisture-Tolerant Zirconium Complex
  • 2020
  • Ingår i: Journal of Organic Chemistry. - : AMER CHEMICAL SOC. - 0022-3263 .- 1520-6904. ; 85:11, s. 6959-6969
  • Tidskriftsartikel (refereegranskat)abstract
    • This work describes the use of kinetics as a tool for rational optimization of an esterification process with down to equimolar ratios of reagents using a recyclable commercially available zirconocene complex in catalytic amounts. In contrast to previously reported group IV metal-catalyzed esterification protocols, the work presented herein circumvents the use of water scavengers and perfluorooctane sulfonate (PFOS) ligands. Insights into the operating mechanism are presented.
  •  
45.
  • Wahlers, J., et al. (författare)
  • Stereoselectivity Predictions for the Pd-Catalyzed 1,4-Conjugate Addition Using Quantum-Guided Molecular Mechanics
  • 2021
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 86:8, s. 5660-5667
  • Tidskriftsartikel (refereegranskat)abstract
    • The conjugate addition of aryl boronic acids to enones is a powerful synthetic tool to introduce quaternary chiral centers, but the experimentally observed stereoselectivities vary widely, and the identification of suitable substrate-ligand combinations requires significant effort. We describe the development and application of a transition-state force field (TSFF) by the quantum-guided molecular mechanics (Q2MM) method that is validated using an automated screen of 9 ligands, 38 aryl boronic acids, and 22 enones, leading to a MUE of 1.8 kJ/mol and a R-2 value of 0.877 over 82 examples. A detailed error analysis identified the structural origin for the deviations in the small group of outliers. The TSFF was then used to predict the stereoselectivity for 27 ligands and 59 enones. The vast majority of the virtual screening results are in line with the expected results. Selected results for 6-substituted pyrox ligands, which were not part of the training set, were followed up by density functional theory and experimental studies.
  •  
46.
  • Wang, Jun, 1983-, et al. (författare)
  • Computational Comparison of Chemical and Isotopic Approaches to Control the Photoisomerization Dynamics of Light-Driven Molecular Motors
  • 2021
  • Ingår i: The Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 86:8, s. 5552-5559
  • Tidskriftsartikel (refereegranskat)abstract
    • Synthetic molecular motors driven by E/Z photoisomerization reactions are able to produce unidirectional rotary motion because of a structural asymmetry that makes one direction of rotation more probable than the other. In most such motors, this asymmetry is realized through the incorporation of a chemically asymmetric carbon atom. Here, we present molecular dynamics simulations based on multiconfigurational quantum chemistry to investigate whether the merits of this approach can be equaled by an alternative approach that instead exploits isotopic chirality. By first considering an N-methylpyrrolidine–cyclopentadiene motor design, it is shown that isotopically chiral variants of this design undergo faster photoisomerizations than a chemically chiral counterpart, while maintaining rotary photoisomerization quantum yields of similarly high magnitude. However, by subsequently considering a pyrrolinium–cyclopentene design, it is also found that the introduction of isotopic chirality does not provide any control of the directionality of the photoinduced rotations within this framework. Taken together, the results highlight both the potential usefulness of isotopic rather than chemical chirality for the design of light-driven molecular motors, and the need for further studies to establish the exact structural circumstances under which this asymmetry is best exploited.
  •  
47.
  • Xu, Yuantai, et al. (författare)
  • Pivotal Electron Delivery Effect of the Cobalt Catalyst in Photocarboxylation of Alkynes : A DFT Calculation
  • 2021
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 86:2, s. 1540-1548
  • Tidskriftsartikel (refereegranskat)abstract
    • Photocarboxylation of alkyne with carbon dioxide represents a highly attractive strategy to prepare functionalized alkenes with high efficiency and atomic economy. However, the reaction mechanism, especially the sequence of elementary steps (leading to different reaction pathways), reaction modes of the H-transfer step and carboxylation step, spin and charge states of the cobalt catalyst, etc., is still an open question. Herein, density functional theory calculations are carried out to probe the mechanism of the Ir/Co-catalyzed photocarboxylation of alkynes. The overall catalytic cycle mainly consists of four steps: reductive-quenching of the Ir catalyst, hydrogen transfer (rate-determining step), outer sphere carboxylation, and the final catalyst regeneration step. Importantly, the cobalt catalyst can facilitate the H-transfer by an uncommon hydride coupled electron transfer (HCET) process. The pivotal electron delivery effect of the Co center enables a facile H-transfer to the alpha-C(alkyne) of the aryl group, resulting in the high regioselectivity for beta-carboxylation.
  •  
48.
  • Zhou, Yixuan, et al. (författare)
  • Effective Organotin-Mediated Regioselective Functionalization of Unprotected Carbohydrates
  • 2023
  • Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 88:11, s. 7174-7151
  • Tidskriftsartikel (refereegranskat)abstract
    • Regioselective functionalization of unprotected carbohydrates at a secondary OH group in the presence of primary OH groups based on the commonly used organotin-mediated reaction has been improved. We found that the preactivation of the dibutylstannylene acetal intermediate with tetrabutylammonium bromide in toluene is a key to the improved condition for the efficient, high-yielding, and regioselective tosylation, benzoylation, or benzylation of unprotected carbohydrates. The counteranion of tetrabutylammonium ion with a weak coordination ability plays a crucial role in the improved regioselective reactions. A convenient access to the intermediates of synthetic value is also demonstrated in the organotin-mediated regioselective tosylation of unprotected carbohydrates, followed by the nucleophilic inversion reaction to give sulfur-containing and azide-modified carbohydrates.
  •  
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