Urea nitrate–catalyzed C‐N and C‐S bond formation: A mechanochemical approach for 5‐chloro‐2‐arylbenzo[d]thiazole derivatives

Par / 24 janvier 2021 / heterocycles
Urea nitrate–catalyzed C‐N and C‐S bond formation: A mechanochemical approach for 5‐chloro‐2‐arylbenzo[d]thiazole derivatives

Abstract

A series of substituted 5‐chloro‐2‐arylbenzo[d]thiazoles were synthesized using 4‐chloro‐2‐aminothiophenol and aromatic aldehydes in the presence of urea nitrate as a catalyst using the mechanochemical grindstone technique. This protocol was effectively carried out under metal‐free conditions at room temperature, and the desired products were obtained in high to excellent yields in short reaction time (30–60 s). The structure of all the synthesized derivatives was confirmed by spectral characterization. The designed protocol has several benefits like eco‐friendly, solvent‐free, high yields, easy workup, and recyclability of catalyst. The catalyst was reusable at least four times without significant loss of activity. The good functional group tolerance with a series of derivatives has been demonstrated.

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Updating the CSIC Reaction (2003–2020)

Par / 22 janvier 2021 / Non classé
Updating the CSIC Reaction (2003–2020)

The mini review describes the progress and developments of the CSIC [Carbanion‐mediated Sulfonate (Sulfonamide) Intermolecular Coupling (or Intramolecular Cyclization)] reaction over the past 17 years, since 2003, when the first thematic review on the CSIC reaction was published.

Abstract

Herein, we have updated the progress and developments of the Carbanion‐mediated Sulfonate (or Sulfonamide) Intermolecular Coupling, and Intramolecular Cyclization, abbreviated as CSIC reaction (CSICr), in the last seventeen years from the seminal review published in 2003 in this same Journal. CSICr has proven to be a useful and versatile synthetic tool, efficiently providing a number of open‐chain [alkane(sulfonamide)sulfonates] or cylic (sultams and sultones) synthetic intermediates or final products of high value in organic and medicinal chemistry.

Wiley: European Journal of Organic Chemistry: Table of Contents
Authors: Alexey V. Dobrydnev, José Marco‐Contelles
doi.org/10.1002/ejoc.202001330

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Non‐Canonical Reactivity of Gold Carbene with Alkyne: An Overview of the Mechanistic Premise

Par / 22 janvier 2021 / Non classé
Non‐Canonical Reactivity of Gold Carbene with Alkyne: An Overview of the Mechanistic Premise

Reactions of gold carbene with alkyne have been discussed with the emphasis on the possible mechanisms, while also focusing on the energetics of the key intermediates as studied in some of the crucial reports covered herein.

Abstract

The unique nature of gold carbene and its synchronous counterpart gold‐stabilized carbocation, is mainly responsible for the non‐canonical reactivity profile that it demonstrates in comparison to any other transition metal carbene. Being an important subset to this class, reactions of gold carbene with alkyne sponsor products far more diverse than cyclopropenation as canonically expected in case of other transition metal carbenes. These gold‐catalyzed reactions have largely been proposed to follow either a [1,n]‐carbene transfer process or an alternate pathway involving a direct interception of the β‐gold vinyl cation with a nucleophile at the cationic carbon. Despite of a clear distinction in structure, bonding and energy of a vinyl gold carbene and β‐gold vinyl cation; they have been found to exhibit identical reactivities like cyclopropenation, C(sp2)–H insertion, etc. making it extremely difficult to “experimentally” investigate and validate a mechanistic pathway. It is because of lack of conclusive experimental evidence, in addition to the limited number of detailed computational studies, that multiple pathways have been proposed simultaneously to rationalize the product formation. As an effort to shed light on the mechanisms of these reactions, herein, documentation of these reactions with a focus on their mechanistic premise has been presented.

Wiley: European Journal of Organic Chemistry: Table of Contents
Authors: Shashank P. Sancheti, Nitin T. Patil
doi.org/10.1002/ejoc.202001528

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Visible‐Light‐Induced Synthesis of 1,2,3,4‐Tetrahydroquinolines through Formal [4+2] Cycloaddition of Acyclic α,β‐Unsaturated Amides and Imides with N,N‐Dialkylanilines

Par / 22 janvier 2021 / Non classé
Visible‐Light‐Induced Synthesis of 1,2,3,4‐Tetrahydroquinolines through Formal [4+2] Cycloaddition of Acyclic α,β‐Unsaturated Amides and Imides with N,N‐Dialkylanilines

Inspired by Greek mythology, Orion is shown in the cover image as a lion‐hearted hunter; he hits acyclic α,β‐unsaturated imides and N,N′‐dialkylanilines with the club to give 1,2,3,4‐tetrahydroquinolines (1,2,3,4‐THQs; the lion fur in the cover image). There are three stars in Orion′s Belt; i.e., ϵ Ori, ζ Ori, and δ Ori, which enhance his toughness. The trio applied to the novel iridium(III) complex photo‐sensitizer, the thiourea, and the azo compound, works cooperatively and powerfully to achieve the photochemical synthesis of structurally diverse 1,2,3,4‐THQs with excellent diastereoselectivity. More information can be found in the Full Paper by K. Itoh, H. Fujii, et al. (DOI: 10.1002/chem.202004186).

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Kennosuke Itoh, Shun‐ichi Nagao, Ken Tokunaga, Shigeto Hirayama, Fumika Karaki, Takaaki Mizuguchi, Kenichiro Nagai, Noriko Sato, Mitsuaki Suzuki, Masashi Hashimoto, Hideaki Fujii
doi.org/10.1002/chem.202100129

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Ultrasound Controlled Anti‐Inflammatory Polarization of Platelet Decorated Microglia for Targeted Ischemic Stroke Therapy

Par / 22 janvier 2021 / Non classé
Ultrasound Controlled Anti‐Inflammatory Polarization of Platelet Decorated Microglia for Targeted Ischemic Stroke Therapy

To realize on‐demand microglia polarization for controllable ischemic stroke therapy, a sono‐sensitive hybrid microglia machine was prepared. Platelet membrane fused microglia have strong accumulation in cerebral vascular injury and can specifically polarize to anti‐inflammatory phenotypes, upon external control by ultrasound irradiation, for angiogenesis and nerve regeneration, leading to survival and behavioral improvement of the stroke mice.

Abstract

Stroke is a lethal cerebral disease with severe sequelae and high mortality. Microglia, the main immune cell in the cerebrum, possess therapeutic potential for strokes as its specific anti‐inflammatory phenotype can reduce inflammation and promote neuron regeneration. However, the on‐demand anti‐inflammatory polarization of microglia at the stroke site is uncontrollable for therapeutic application. Here, we develop a platelet hybrid microglia platform which can specifically polarize to the anti‐inflammatory phenotype by ultrasound irradiation for targeted cerebrum repair after stroke. The engineered microglia have strong adherence to the injured cerebral vessels with platelet membrane fusion and realize on‐demand anti‐inflammatory polarization with ultrasound‐responsive IL‐4 liposome decoration. The intravenously injected microglia platform showed anti‐inflammatory polarization at the stroke site with insonation, and accelerated the M2‐type polarization of endogenous microglia for long‐term stroke recovery. Satisfied prognoses were achieved with reduced apoptosis, promoted neurogenesis, and functional recovery, indicating the implications of the microglia platform for stroke therapy.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Yujie Li, Xucong Teng, Chunrong Yang, Yongji Wang, Lingxiao Wang, Yicong Dai, Hua Sun, Jinghong Li
doi.org/10.1002/anie.202010391

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To Every Rule There is an Exception: A Rational Extension of Loewenstein’s Rule

Par / 22 janvier 2021 / Non classé
To Every Rule There is an Exception: A Rational Extension of Loewenstein's Rule

According to Loewenstein’s rule Al−O−Al motifs are energetically unstable in zeolites; here, using atomic scale simulations, the limitations of this rule are demonstrated and a rational extension is shown.

Abstract

Loewenstein’s rule, which states that Al−O−Al motifs are energetically unstable, is fundamental to the understanding and design of zeolites. Here, using a combination of electronic structure calculations and lattice models, we show under which circumstances this rule becomes invalid and how it can be rationally extended using the chabasite framework for demonstration.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Magnus Fant, Mattias Ångqvist, Anders Hellman, Paul Erhart
doi.org/10.1002/anie.202013256

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Triazenyl Alkynes as Versatile Building Blocks in Multicomponent Reactions: Diastereoselective Synthesis of β‐Amino Amides

Par / 22 janvier 2021 / Non classé
Triazenyl Alkynes as Versatile Building Blocks in Multicomponent Reactions: Diastereoselective Synthesis of β‐Amino Amides

Triazenyl alkynes serve as versatile building blocks in multicomponent reactions for diastereoselective synthesis of β‐amino amides. The alkyne moiety acts as C2 fragment and the triazene group serves as directing group to modulate the transition state thus to achieve both chemical reactivity and diastereoselectivity. The triazene group also enables late‐stage transformation. Diverse β‐amino amides were rapidly assembled in an operational simple and atom‐economic process.

Abstract

Multicomponent reactions (MCRs) are powerful tool for the construction of polyfunctional molecules in an operationally simple and atom‐economic manner, and the discovery of novel MCRs requests various building blocks. Herein, triazenyl alkynes were disclosed as versatile building blocks in a multicomponent reaction with carboxylic acids, aldehydes and anilines to furnish β‐amino amides with the achievement of high diastereoselectivity and structural diversity. In this process, triazenyl alkynes were bifunctional so that the alkyne moiety acts as C2 fragment and triazene serves as directing group to modulate the transition state thus achieving high diastereoselectivity, in consistence with DFT calculations. Furthermore, the triazenyl group also enables diverse late‐stage transformation. This protocol opens a new vision for the discovery of building block and rational design of MCRs.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Chaorong Wang, Zhencheng Lai, Hujun Xie, Sunliang Cui
doi.org/10.1002/anie.202014686

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Formic Acid‐Assisted Selective Hydrogenolysis of 5‐Hydroxymethylfurfural to 2,5‐Dimethylfuran over Bifunctional Pd Nanoparticles Supported on N‐Doped Mesoporous Carbon

Par / 22 janvier 2021 / Non classé
Formic Acid‐Assisted Selective Hydrogenolysis of 5‐Hydroxymethylfurfural to 2,5‐Dimethylfuran over Bifunctional Pd Nanoparticles Supported on N‐Doped Mesoporous Carbon

Quantitative conversion of HMF to DMF was achieved in the presence of formic acid and H2 over the bifunctional Pd/NMC catalyst within 2 h. Experimental investigation and DFT calculation revealed that formic acid significantly enhances the reaction rate and shifts the dominant reaction pathway from the hydrogenation of the aldehyde group to the hydrogenolysis of the hydroxymethyl group via its protonation.

Abstract

Biomass‐derived 5‐hydroxymethylfurfural (HMF) is regarded as one of the most promising platform chemicals to produce 2,5‐dimethylfuran (DMF) as a potential liquid transportation fuel. Pd nanoparticles supported on N‐containing and N‐free mesoporous carbon materials were prepared, characterized, and applied in the hydrogenolysis of HMF to DMF under mild reaction conditions. Quantitative conversion of HMF to DMF was achieved in the presence of formic acid (FA) and H2 over Pd/NMC within 2 h. The reaction mechanism, especially the multiple roles of FA, was explored through a detailed comparative study by varying hydrogen source, additive, and substrate as well as by applying in situ ATR‐IR spectroscopy. The major role of FA is to shift the dominant reaction pathway from the hydrogenation of the aldehyde group to the hydrogenolysis of the hydroxymethyl group via the protonation by FA at the C‐OH group, lowering the activation barrier of the C−O bond cleavage and thus significantly enhancing the reaction rate. XPS results and DFT calculations revealed that Pd2+ species interacting with pyridine‐like N atoms significantly enhance the selective hydrogenolysis of the C−OH bond in the presence of FA due to their high ability for the activation of FA and the stabilization of H−.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Bin Hu, Lisa Warczinski, Xiaoyu Li, Mohong Lu, Johannes Bitzer, Markus Heidelmann, Till Eckhard, Qi Fu, Jonas Schulwitz, Mariia Merko, Mingshi Li, Wolfgang Kleist, Christof Hättig, Martin Muhler, Baoxiang Peng
doi.org/10.1002/anie.202012816

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Optochemical Control of DNA‐Switching Circuits for Logic and Probabilistic Computation

Par / 22 janvier 2021 / Non classé
Optochemical Control of DNA‐Switching Circuits for Logic and Probabilistic Computation

In this work, we report optochemically controlled DNA switching circuits for regulating computation functions, including multiple logic computation and probabilistic computation.

Abstract

Precise control of DNA‐circuit functions facilitates the construction of complex DNA networks to perform sophisticated functions. Inspired by optochemical genetics with high precision for controlling and studying neural networks by photoregulation of membrane receptors, we herein report optochemically controlled DNA switching circuits for regulating computation functions. The DNA‐switching circuits involve a CG–C+ triplex‐based DNA switch that undergoes structural transition from triplex to duplex states after exposure to UV irradiation due to proton transfer, showing optochemical control. We demonstrate that the DNA‐switching circuits enable the regulation of computation functions by optochemical control of the state of the DNA switch, including multiple logic computations and probabilistic computation. We hope this work will broaden DNA‐circuit functions and facilitate the construction of complex DNA networks.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Xiewei Xiong, Mingshu Xiao, Wei Lai, Li Li, Chunhai Fan, Hao Pei
doi.org/10.1002/anie.202013883

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Evolution of the Diels–Alder Reaction Mechanism since the 1930s: Woodward, Houk with Woodward, and the Influence of Computational Chemistry on Understanding Cycloadditions

Par / 22 janvier 2021 / Non classé
Evolution of the Diels–Alder Reaction Mechanism since the 1930s: Woodward, Houk with Woodward, and the Influence of Computational Chemistry on Understanding Cycloadditions

The evolution of understanding of the Diels–Alder reaction mechanism is described, from R. B. Woodward’s boyhood visions, to Ken Houk’s experiences as a graduate student in Woodward’s laboratory, to today’s dynamical view of Diels–Alder and higher‐order cycloadditions. Roald Hoffmann’s Coda gives his view of Woodward and the zig‐zag processes of scientific discovery.

Abstract

This review article describes the evolution of Woodward’s mechanistic thinking, beginning in the late 1930s and early 1940s with his proposal of a charge‐transfer mechanism for the Diels–Alder reaction, eventually leading to the Woodward–Katz two‐stage concerted mechanism in 1959, and then to its mechanistic solution in terms of orbital symmetry control. Houk′s research in the Woodward labs, testing the predictions of this theory, is described. Subsequent modern calculations with quantum mechanics and molecular dynamics simulations have shown that Woodward indeed had perfectly described not only the cyclopentadiene dimerization mechanism, but a new class of transition states now known as ambimodal or bis‐pericyclic transition states. In recent years, the Houk group has found that ambimodal reactions are operative in the [6+4] cycloaddition. Molecular dynamics simulations of many Diels–Alder and ambimodal cycloadditions provide a time‐resolved picture of how these reactions occur. Lastly, Roald Hoffmann provides a Coda in which he describes his joy in “being taken along the journey” of the cycloaddition story from Woodward’s youth to today’s trajectory simulations.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Kendall N. Houk, Fang Liu, Zhongyue Yang, Jeffrey I. Seeman
doi.org/10.1002/anie.202001654

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Boron in Prebiological Evolution

Par / 22 janvier 2021 / Non classé
Boron in Prebiological Evolution

Research suggests that borate could have mediated the prebiotic synthesis of RNA precursors (ribose, ribonucleosides, and ribonucleotides) in reactions relevant for the origin of life. This minireview provides an overview of recent developments in prebiological chemistry related to boron species.

Abstract

Boron(III), as borate (or boric acid), mediates the synthesis of ribose, ribonucleosides, and ribonucleotides. These reactions are carried out under moderate temperatures (typically 70–95 °C) with organic molecules (or their derivatives) detected in interstellar space and inorganic ions found in minerals on Earth (and could occur during early stages of prebiotic evolution). Research in this century suggests that borate was a relevant prebiological reagent, thus reinforcing the RNA world hypothesis as an explanation for the origin of life. Herein, these developments on prebiological chemistry related to boron species are reviewed.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Ana Franco, José Armando L. Silva
doi.org/10.1002/anie.202010616

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Synthesis of Trifluoromethylated Dithiocarbamates via Photocatalyzed Substitution Reaction: Pentafluoropyridine as Activating Reagent

Par / 22 janvier 2021 / Non classé
Synthesis of Trifluoromethylated Dithiocarbamates via Photocatalyzed Substitution Reaction: Pentafluoropyridine as Activating Reagent

Trifluoromethylation of aldehydes with subsequent derivatization using pentafluoropyridine provides pyridinyl ethers which undergo light mediated substitution by dithiocarbamate anion, affording fluorinated dithiocarbamates.

Abstract

A method for the synthesis of trifluoromethyl‐substituted dithiocarbamates from aldehydes is described. The reaction involves nucleophilic trifluoromethylation, derivatization of the silyloxy‐group with pentafluoropyridine, and substitution of the fluorinated pyridinyloxy group by dithiocarbamate anion. The substitution step is performed in the presence of 12‐phenyl‐12H‐benzo[b]phenothiazine and copper cyanide under irradiation of 400 nm LED.

Wiley: European Journal of Organic Chemistry: Table of Contents
Authors: Artem A. Zemtsov, Sergey S. Lunkov, Vitalij V. Levin, Alexander D. Dilman
doi.org/10.1002/ejoc.202001572

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Oxidative Transformation of Biomass into Formic Acid

Par / 22 janvier 2021 / Non classé
Oxidative Transformation of Biomass into Formic Acid

Formic acid is receiving attention as a promising hydrogen source as well as a valuable chemical for the industries of textiles, pharmaceuticals etc. This minireview is focused on the recent advancement in its formation from biomass, using oxidative pathways and different catalysts such as polyoxometalate, vanadium oxide, hydrothermal, and photocatalysis, developed over the past ten years.

Abstract

Formic acid (FA) is well‐known as a promising hydrogen source as well as a valuable chemical for the industries of textiles, pharmaceuticals etc. In fact, 1.137 million metric tons of FA is required worldwide per year to meet the current demand. Therefore, there is a strong interest for the generation of FA in a sustainable way to meet the future demand. Inspired by this information, several strategies have been considered for the sustainable synthesis of FA. Herein, we summarise the recent articles for the oxidative transformation of biomass into FA.

Wiley: European Journal of Organic Chemistry: Table of Contents
Authors: Prakash Kumar Sahoo, Tong Zhang, Shoubhik Das
doi.org/10.1002/ejoc.202001514

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Stimuli‐Responsive Self‐Sorting Hybrid Hydrogen‐Bonded/Metal‐Coordinated Cage

Par / 22 janvier 2021 / Non classé
Stimuli‐Responsive Self‐Sorting Hybrid Hydrogen‐Bonded/Metal‐Coordinated Cage

Caged: A self‐assembled hybrid hydrogen‐bonded/metal‐coordinated cage, where both hydrogen‐bonding and metal‐coordination form the crucial part of the topology. The hybrid cage is prepared combining hydrogen‐bonded rosette motif and palladium(II)/platinum(II) coordination to a pyridine ligand.

Abstract

The self‐assembly of a unique molecular container is reported: a hybrid hydrogen‐bonded/metal‐coordinated cage where both hydrogen‐bonding and metal‐coordination form the crucial part of the topology. The hybrid cage was prepared combining hydrogen‐bonded rosette motif and palladium(II)/platinum(II) coordination to a pyridine ligand. It was also shown that the hybrid cage could be prepared by integrative self‐sorting from simple components. For the first time the genuine dual character of the hybrid cage was manifested as both self‐assembling parts responded selectively to different stimuli (such as phosphine and cyanurate), which resulted in the disassembly of the cage.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Petr Motloch, Christopher A. Hunter
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202005283

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Novel, Chiral, and Enantiopure C2‐Symmetric Thioureas Promote Asymmetric Protio‐Pictet‐Spengler Reactions by Anion‐Binding Catalysis

Par / 22 janvier 2021 / Non classé
Novel, Chiral, and Enantiopure C2‐Symmetric Thioureas Promote Asymmetric Protio‐Pictet‐Spengler Reactions by Anion‐Binding Catalysis

A novel L‐valine‐derived C2‐symmetric thiourea catalyst, in combination with 4‐methoxybenzoic acid, promoted the enantioselective reaction of tryptamines with aldehydes (protio‐Pictet‐Spengler reactions) to give the corresponding tetrahydro‐β‐carbolines with good enantioselectivity (up to 95 % ee) by chiral anion‐binding catalysis.

Abstract

Although anion‐binding processes are well‐known for their crucial role in molecular recognition, they have only recently been utilized for catalysis. Herein, a new class of chiral, enantiopure C2‐symmetrical thioureas that, in combination with 4‐methoxybenzoic acid, promotes the enantioselective protio‐Pictet‐Spengler reaction to provide unprotected tetrahydro‐β‐carbolines in good yields (40–93 %) and moderate‐to‐high enantioselectivities (34–95 % ee) in one step from tryptamine and aldehyde derivatives is described. The formation of a chiral catalyst‐anion complex was explored by 1H NMR.

Wiley: European Journal of Organic Chemistry: Table of Contents
Authors: Michele Retini, Francesca Bartoccini, Giovanni Zappia, Giovanni Piersanti
doi.org/10.1002/ejoc.202001501

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Forty Years after the Discovery of Its Nucleolytic Activity: [Cu(phen)2]2+ Shows Unattended DNA Cleavage Activity upon Fluorination

Par / 22 janvier 2021 / Non classé
Forty Years after the Discovery of Its Nucleolytic Activity: [Cu(phen)2]2+ Shows Unattended DNA Cleavage Activity upon Fluorination

Activation by fluorination: By introducing fluorine‐containing substituents in the 1,10‐phenanthroline ligands of a [Cu(phen)2]2+ complex, nucleolytic activity in the absence of classical, bioabundant external reducing agents is observed. Such an activity is unknown for the unsubstituted [Cu(phen)2]2+, the first and otherwise one of the most efficient artificial nucleases. Also, the cytotoxicity profiles of the new complexes were different—though less toxic, cancer cells were more harmed than healthy cells.

Abstract

[Cu(phen)2]2+ (phen=1,10‐phenanthroline) is the first and still one of the most efficient artificial nucleases. In general, when the phen ligand is modified, the nucleolytic activity of its CuII complex is significantly reduced. This is most likely due to higher steric bulk of such ligands and thus lower affinity to DNA. CuII complexes with phen ligands having fluorinated substituents (F, CF3, SF5, SCF3) surprisingly showed excellent DNA cleavage activity—in contrast to the unsubstituted [Cu(phen)2]2+—in the absence of the otherwise required classical, bioabundant external reducing agents like thiols or ascorbate. This nucleolytic activity correlates well with the half‐wave potentials E1/2 of the complexes. Cancer cell studies show cytotoxic effects of all complexes with fluorinated ligands in the low μm range, whereas they were less toxic towards healthy cells (fibroblasts).

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Carsten Lüdtke, Sebastian Sobottka, Julian Heinrich, Phil Liebing, Stefanie Wedepohl, Biprajit Sarkar, Nora Kulak
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004594

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Synthesis and Determination of Absolute Configuration of Zealexin A1, a Sesquiterpenoid Phytoalexin from Zea mays

Par / 22 janvier 2021 / Non classé
Synthesis and Determination of Absolute Configuration of Zealexin A1, a Sesquiterpenoid Phytoalexin from Zea mays

The enantioselective synthesis of zealexin A1, a macrocarpane‐type sesquiterpene phytoalexin is described. Our methodology for the total synthesis involved the stereoselective construction of the stereogenic center via enzymatic resolution followed by Johnson–Claisen rearrangement. The absolute configuration of the natural product was determined by GC analyses of the synthetic and natural zealexin A1 methyl esters.

Abstract

The enantioselective synthesis of zealexin A1, a sesquiterpene phytoalexin isolated from maize Zea mays is described for the first time. Our methodology for the total synthesis of zealexin A1 involved the stereoselective construction of the stereogenic center via enzymatic resolution followed by Johnson–Claisen rearrangement. The absolute configuration of the natural product was determined through gas chromatography analyses for the methyl esters for both synthetic and natural zealexin A1.

Wiley: European Journal of Organic Chemistry: Table of Contents
Authors: Arata Yajima, Mikaho Shimura, Tatsuo Saito, Ryo Katsuta, Ken Ishigami, Alisa Huffaker, Eric A. Schmelz
doi.org/10.1002/ejoc.202001596

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Rhodium‐Catalyzed Chemodivergent Regio‐ and Enantioselective Allylic Alkylation of Indoles

Par / 22 janvier 2021 / Non classé
Rhodium‐Catalyzed Chemodivergent Regio‐ and Enantioselective Allylic Alkylation of Indoles

C3 or N1? Chemodivergent regio‐ and enantioselective allylic alkylation of indoles was developed by using a rhodium/bisoxazolinephosphane catalyst. C3 or N1 selectivity could be selectively achieved by changing the counteranion of Rh, the allylic carbonate, the reaction temperature, and the ligand.

Abstract

The control of C3/N1 chemoselectivity in indole alkylation with the same electrophiles is still challenging. An Rh/bisoxazolinephosphane‐catalyzed chemodivergent regio‐ and enantioselective allylic alkylation of indoles was developed. Chiral C3‐ and N1‐allylindoles can be selectively obtained with high branched/linear ratio and up to 99 % ee by changing the counteranion of Rh, the allylic carbonate, the reaction temperature, and the ligand.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Minghe Sun, Min Liu, Changkun Li
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004613

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Zinc Oxide Defect Microstructure and Surface Chemistry Derived from Oxidation of Metallic Zinc: Thin‐Film Transistor and Sensor Behavior of ZnO Films and Rods

Par / 22 janvier 2021 / Non classé
Zinc Oxide Defect Microstructure and Surface Chemistry Derived from Oxidation of Metallic Zinc: Thin‐Film Transistor and Sensor Behavior of ZnO Films and Rods

Thin‐film transistors: Zinc oxide layers can be obtained conveniently through the oxidation of sputter‐deposited thin films of zinc metal at temperatures between 250 and 450 °C. Positron annihilation studies hint at vacancy clusters rather than isolated point defects as the dominating feature in the defect chemistry of these films. This allows the description of the influence of annealing temperature on the resulting electronic performance of the semiconducting layers in thin‐film transistors.

Abstract

Zinc oxide thin films are fabricated by controlled oxidation of sputtered zinc metal films on a hotplate in air at temperatures between 250 and 450 °C. The nanocrystalline films possess high relative densities and show preferential growth in (100) orientation. Integration in thin‐film transistors reveals moderate charge carrier mobilities as high as 0.2 cm2 V−1s−1. The semiconducting properties depend on the calcination temperature, whereby the best performance is achieved at 450 °C. The defect structure of the thin ZnO film can be tracked by Doppler‐broadening positron annihilation spectroscopy as well as positron lifetime studies. Comparably long positron lifetimes suggest interaction of zinc vacancies (VZn) with one or more oxygen vacancies (VO) in larger structural entities. Such VO‐VZn defect clusters act as shallow acceptors, and thus, reduce the overall electron conductivity of the film. The concentration of these defect clusters decreases at higher calcination temperatures as indicated by changes in the S and W parameters. Such zinc oxide films obtained by conversion of metallic zinc can also be used as seed layers for solution deposition of zinc oxide nanowires employing a mild microwave‐assisted process. The functionality of the obtained nanowire arrays is tested in a UV sensor device. The best results with respect to sensor sensitivity are achieved with thinner seed layers for device construction.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Rudolf C. Hoffmann, Shawn Sanctis, Maciej O. Liedke, Maik Butterling, Andreas Wagner, Christian Njel, Jörg J. Schneider
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004270

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The Riveting Chemistry of Poly‐aza‐heterocycles Employing Microwave Technique: A Decade Review

Par / 22 janvier 2021 / Non classé
The Riveting Chemistry of Poly‐aza‐heterocycles Employing Microwave Technique: A Decade Review

The present review discloses microwave‐assisted chemistry of five/six‐member poly‐aza‐heterocycles namely, triazole, tetrazole, triazine, and tetrazine. The emphasis has been made towards the advantages of microwave conditions over conventional process. The review unveils the latest synthetic approaches and potential applications originated from these heterocycles.

Abstract

The application of microwave technique in chemical laboratory rooted back in 1986 and found advantageous over conventional approaches. On the other side, poly‐aza‐heterocycles are influencing organic frameworks with a fascinating chemistry and well explored by employing microwave‐assisted organic reactions. In the present review, we have thoroughly updated rousing literatures of microwave‐assisted synthesis and reactions of various poly‐aza‐heterocycles viz., triazole, tetrazole, triazine, and tetrazine from the past decade (2010–2020). The expedient chemistry and enabling role of microwave heating for adequate chemical transformations of such heterocycles, which were more challenging using classical approaches, are appropriately elucidated. This review also highlights the potential applications of these heterocyclic scaffolds and their derivatives in different scientific domains. Remarkably, such chemical architects possess wide applications as crucial building blocks in synthesis of biologically relevant compounds, agrochemicals, and compounds of interest in material science.

Wiley: European Journal of Organic Chemistry: Table of Contents
Authors: Jay Prakash Soni, Swanand Vinayak Joshi, Krishna Sowjanya Chemitikanti, Nagula Shankaraiah
doi.org/10.1002/ejoc.202001472

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Twisting Versus Delocalization in CAAC‐ and NHC‐Stabilized Boron‐Based Biradicals: The Roles of Sterics and Electronics

Par / 22 janvier 2021 / Non classé
Twisting Versus Delocalization in CAAC‐ and NHC‐Stabilized Boron‐Based Biradicals: The Roles of Sterics and Electronics

Boron chemistry offers many systems in which slight variations lead to drastic geometrical and electronic perturbations. This article explains the reasons for variations observed in a system consisting of two boron centers stabilized by CAAC or NHC donors and connected by C2R2 (R=Et, Me, H) bridges. For CAAC and R=Me, Et the bridge is twisted, and the molecule is a biradical. For CAAC and R=H the bridge is not twisted, leading to a closed‐shell structure. For NHC‐stabilized systems we predict closed‐shell molecules with partially twisted bridges. This is attributed to a delicate interplay of steric and electronic effects. More information can be found in the Full Paper by B. Engels et al. (DOI: 10.1002/chem.202004619).

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Paul Schmid, Felipe Fantuzzi, Jonas Klopf, Niklas B. Schröder, Rian D. Dewhurst, Holger Braunschweig, Volker Engel, Bernd Engels
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202005225

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Nickel‐ and Palladium‐Catalyzed Cross‐Coupling of Aryl Fluorosulfonates and Phosphites: Synthesis of Aryl Phosphonates

Par / 22 janvier 2021 / Non classé
Nickel‐ and Palladium‐Catalyzed Cross‐Coupling of Aryl Fluorosulfonates and Phosphites: Synthesis of Aryl Phosphonates

An efficient palladium or nickel‐catalyzed C(sp2)−P bond formation proceeds with excellent yields under mild conditions. Direct conversion of phenol to aryl phosphonates in a single pot has been developed. Broad functional group compatibility enables the economical preparation of organophosphorus compounds.

Abstract

The synthesis of aryl phosphonates via nickel and palladium‐catalyzed cross‐coupling of aryl fluorosulfonates and phosphites is described. The products were obtained in good to excellent yields under mild conditions with broad functional group compatibility, employing either Pd(OAc)2 and DPEPhos or the readily available NiCl2(dme) and Xantphos as catalytic systems. Noteworthily, the present C(sp2)−P bond formation method could be applied to the direct conversion of phenols to the corresponding aryl phosphonates in one pot via reaction of phenols with SO2F2 and subsequent palladium‐catalyzed cross‐coupling.

Wiley: European Journal of Organic Chemistry: Table of Contents
Authors: Guofu Zhang, Jing Wang, Chenfei Guan, Yiyong Zhao, Chengrong Ding
doi.org/10.1002/ejoc.202001485

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Klyflaccilins B‐T, Polyoxgenated Eunicellins from the Soft Coral Klyxum flaccidum

Par / 22 janvier 2021 / Non classé
Klyflaccilins B‐T, Polyoxgenated Eunicellins from the Soft Coral Klyxum flaccidum

Nineteen new eunicellin diterpenoids named klyflaccilins B‐T were isolated from the gorgonian Klyxum flaccidum. The structures were elucidated by NMR, showing that they represent different eunicellin subclasses. For five compounds X‐ray crystal structures were obtained that allowed to determine their absolute configurations.

Abstract

Nineteen polyoxygenated eunicellin diterpenoids, named klyflaccilins B‐T (1–19), were isolated from the South China Sea soft coral Klyxum flaccidum. Their structures were established by extensive spectroscopic analysis and for several of the isolated compounds the absolute configurations were determined by X‐ray diffraction analysis.

Wiley: European Journal of Organic Chemistry: Table of Contents
Authors: Geng Li, Li‐Li Sun, Jeroen S. Dickschat, Yue‐Wei Guo
doi.org/10.1002/ejoc.202001647

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2,3‐Dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ)‐Mediated Tandem Oxidative Annulation for Preparing 2,2‐Disubstituted 2,3‐Dihydroquinazolin‐4(1H)‐ones

Par / 22 janvier 2021 / Non classé
2,3‐Dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ)‐Mediated Tandem Oxidative Annulation for Preparing 2,2‐Disubstituted 2,3‐Dihydroquinazolin‐4(1H)‐ones

The tandem oxidative annulation of o‐aminobenzamides and 1,3‐diarylpropenes was mediated by DDQ via dual cross‐dehydrogenative‐coupling (CDC) reactions. It provides an efficient and convenient method for the synthesis of 2,2‐disubstituted 2,3‐dihydroquinazolin‐4(1H)‐ones.

Abstract

An efficient tandem oxidative annulation for the synthesis of 2,2‐disubstituted 2,3‐dihydroquinazolin‐4(1H)‐ones via DDQ‐mediated dual cross‐dehydrogenative‐coupling (CDC) reactions is described. This transformation proceeds from easily available o‐aminobenzamides and 1,3‐diarylpropenes under mild conditions, and the corresponding products are obtained in moderate to excellent yields.

Wiley: European Journal of Organic Chemistry: Table of Contents
Authors: Dongping Cheng, Xianhang Yan, Yueqi Pu, Jing Shen, Xiaoliang Xu, Jizhong Yan
doi.org/10.1002/ejoc.202001479

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Tris(5‐aryl‐1,3,4‐oxadiazolyl)benzotrithiophenes – Discotic Liquid Crystals with Enormous Mesophase Ranges

Par / 22 janvier 2021 / Non classé
Tris(5‐aryl‐1,3,4‐oxadiazolyl)benzotrithiophenes – Discotic Liquid Crystals with Enormous Mesophase Ranges

C3‐symmetrical stars with a heterocyclic core and a periphery of six to nine alkoxy chains are synthesized via Huisgen reaction. DSC, POM, and TGA give information about the thermal properties of these discotic liquid crystals, XRD enlightens the structures of the very broad mesophases The efficient fluorescence of these discs is positively solvatochromic and strongly influenced by aggregation.

Abstract

C3‐symmetrical, alkoxyphenyl substituted 2,5,8‐(tris‐1,3,4‐oxadiazol‐2‐yl)benzo [1,2‐b; 3,4‐b′; 5,6‐b′′]trithiophenes (OXD‐BTT) are synthesized via threefold Huisgen‐reaction. A broad variation of alkoxy substitution pattern and chain lengths is reported. The thermal behavior was investigated via differential scanning calorimetry (DSC), polarized optical microscopy (POM) and thermogravimetry (TGA). Optical properties were studied via UV‐Vis and fluorescence spectroscopy. Structural information of the LC phases was gained from X‐ray diffraction on oriented fibers. OXD‐BTT provide enormous phase widths (ΔT≥289 K) with clearing points close to thermal decomposition. Most of the derivatives exhibit two different mesophases, the lower phase with a rectangular 3D‐structure and a hexagonal 2D‐lattice at higher temperature. The variation of the chain length allows a tuning of melting and clearing points. OXD‐BTT emit blue light with fluorescence quantum yields up to 30 % in good solvents. The emission is very sensitive to aggregation, thus, in poor solvents the emission intensity decreases, and red shift of maxima occurs.

Wiley: European Journal of Organic Chemistry: Table of Contents
Authors: Natalie Tober, Johannes Winter, Matthias Jochem, Matthias Lehmann, Heiner Detert
doi.org/10.1002/ejoc.202001475

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