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Beilstein Journal of Organic Chemistry

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https://www.readbyqxmd.com/read/28904627/mechanochemical-synthesis-of-thioureas-ureas-and-guanidines
#1
REVIEW
Vjekoslav Štrukil
In this review, the recent progress in the synthesis of ureas, thioureas and guanidines by solid-state mechanochemical ball milling is highlighted. While the literature is abundant on their preparation in conventional solution environment, it was not until the advent of solvent-free manual grinding using a mortar and pestle and automated ball milling that new synthetic opportunities have opened. The mechanochemical approach not only has enabled the quantitative synthesis of (thio)ureas and guanidines without using bulk solvents and the generation of byproducts, but it has also been established as a means to develop "click-type" chemistry for these classes of compounds and the concept of small molecule desymmetrization...
2017: Beilstein Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28904626/iodoarene-catalyzed-cyclizations-of-n-propargylamides-and-%C3%AE-amidoketones-synthesis-of-2-oxazolines
#2
Somaia Kamouka, Wesley J Moran
Two complementary iodoarene-catalyzed methods for the preparation of 2-oxazolines are presented. The first involves the cyclization of N-propargylamides and the second involves the cyclization of β-amidoketones. These are proposed to proceed through different mechanisms and have different substrate scopes.
2017: Beilstein Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28904625/nhc-catalyzed-cleavage-of-vicinal-diketones-and-triketones-followed-by-insertion-of-enones-and-ynones
#3
Ken Takaki, Makoto Hino, Akira Ohno, Kimihiro Komeyama, Hiroto Yoshida, Hiroshi Fukuoka
Thiazolium carbene-catalyzed reactions of 1,2-diketones and 1,2,3-triketones with enones and ynones have been investigated. The diketones gave α,β-double acylation products via unique Breslow intermediates isolable as acid salts, whereas the triketones formed stable adducts with the NHC instead of the coupling products.
2017: Beilstein Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28904624/pd-oac-2-ph3p-catalyzed-dimerization-of-isoprene-and-synthesis-of-monoterpenic-heterocycles
#4
Dominik Kellner, Maximilian Weger, Andrea Gini, Olga García Mancheño
The palladium-catalyzed dimerization of isoprene is a practical approach of synthesizing monoterpenes. Though several highly selective methods have been reported, most of them still required pressure or costly ligands for attaining the active system and desired selectivity. Herein, we present a simple and economical procedure towards the tail-to-tail dimer using readily available Pd(OAc)2 and inexpensive triphenylphosphine as ligand. Furthermore, simple screw cap vials are employed, allowing carrying out the reaction at low pressure...
2017: Beilstein Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28904623/ni-nanoparticles-on-rgo-as-reusable-heterogeneous-catalyst-effect-of-ni-particle-size-and-intermediate-composite-structures-in-c-s-cross-coupling-reaction
#5
Debasish Sengupta, Koushik Bhowmik, Goutam De, Basudeb Basu
The present work demonstrates the C-S cross-coupling reaction between aryl halides and thiols using nickel nanoparticles (Ni NPs) supported on reduced graphene oxide (Ni/RGO) as a heterogeneous catalyst. It is observed that the uniformly dispersed Ni NPs supported on RGO could exhibit excellent catalytic activity in C-S cross-coupling reactions and the catalytic application is generalized with diverse coupling partners. Although the electron-rich planar RGO surface helps in stabilizing the agglomeration-free Ni NPs, the catalytic process is found to occur involving Ni(II) species and the recovered catalyst containing both Ni(0)/Ni(II) species is equally efficient in recycle runs...
2017: Beilstein Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28904622/selective-enzymatic-esterification-of-lignin-model-compounds-in-the-ball-mill
#6
Ulla Weißbach, Saumya Dabral, Laure Konnert, Carsten Bolm, José G Hernández
A lipase-catalyzed esterification of lignin model compounds in the ball mill was developed combining the advantages of enzyme catalysis and mechanochemistry. Under the described conditions, the primary aliphatic hydroxy groups present in the substrates were selectively modified by the biocatalyst to afford monoesterified products. Amongst the tested lipases, CALB proved to be the most effective biocatalyst for these transformations. Noteworthy, various acyl donors of different chain lengths were tolerated under the mechanochemical conditions...
2017: Beilstein Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28904621/conformational-impact-of-structural-modifications-in-2-fluorocyclohexanone
#7
Francisco A Martins, Josué M Silla, Matheus P Freitas
2-Haloketones are building blocks that combine physical, chemical and biological features of materials and bioactive compounds, while organic fluorine plays a fundamental role in the design of performance organic molecules. Since these features are dependent on the three-dimensional chemical structure of a molecule, simple structural modifications can affect its conformational stability and, consequently, the corresponding physicochemical/biological property of interest. In this work, structural changes in 2-fluorocyclohexanone were theoretically studied with the aim at finding intramolecular interactions that induce the conformational equilibrium towards the axial or equatorial conformer...
2017: Beilstein Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28904620/18-hydroxydolabella-3-7-diene-synthase-a-diterpene-synthase-from-chitinophaga-pinensis
#8
Jeroen S Dickschat, Jan Rinkel, Patrick Rabe, Arman Beyraghdar Kashkooli, Harro J Bouwmeester
The product obtained in vitro from a diterpene synthase encoded in the genome of the bacterium Chitinophaga pinensis, an enzyme previously reported to have germacrene A synthase activity during heterologous expression in Escherichia coli, was identified by extensive NMR-spectroscopic methods as 18-hydroxydolabella-3,7-diene. The absolute configuration of this diterpene alcohol and the stereochemical course of the terpene synthase reaction were addressed by isotopic labelling experiments. Heterologous expression of the diterpene synthase in Nicotiana benthamiana resulted in the production of 18-hydroxydolabella-3,7-diene also in planta, while the results from the heterologous expression in E...
2017: Beilstein Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28904619/chiral-phase-transfer-catalysis-in-the-asymmetric-%C3%AE-heterofunctionalization-of-prochiral-nucleophiles
#9
REVIEW
Johannes Schörgenhumer, Maximilian Tiffner, Mario Waser
Chiral phase-transfer catalysis is one of the major catalytic principles in asymmetric catalysis. A broad variety of different catalysts and their use for challenging applications have been reported over the last decades. Besides asymmetric C-C bond forming reactions the use of chiral phase-transfer catalysts for enantioselective α-heterofunctionalization reactions of prochiral nucleophiles became one of the most important field of application of this catalytic principle. Based on several highly spectacular recent reports, we thus wish to discuss some of the most important achievements in this field within the context of this review...
2017: Beilstein Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28904618/mechanochemical-n-alkylation-of-imides
#10
Anamarija Briš, Mateja Đud, Davor Margetić
The mechanochemical N-alkylation of imide derivatives was studied. Reactions under solvent-free conditions in a ball mill gave good yields and could be put in place of the classical solution conditions. The method is general and can be applied to various imides and alkyl halides. Phthalimides prepared under ball milling conditions were used in a mechanochemical Gabriel synthesis of amines by their reaction with 1,2-diaminoethane.
2017: Beilstein Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28904617/an-efficient-pd-nhc-catalyst-system-in-situ-generated-from-na2pdcl4-and-peg-functionalized-imidazolium-salts-for-mizoroki-heck-reactions-in-water
#11
Nan Sun, Meng Chen, Liqun Jin, Wei Zhao, Baoxiang Hu, Zhenlu Shen, Xinquan Hu
Three PEG-functionalized imidazolium salts L1-L3 were designed and prepared from commercially available materials via a simple method. Their corresponding water soluble Pd-NHC catalysts, in situ generated from the imidazolium salts L1-L3 and Na2PdCl4 in water, showed impressive catalytic activity for aqueous Mizoroki-Heck reactions. The kinetic study revealed that the Pd catalyst derived from the imidazolium salt L1, bearing a pyridine-2-methyl substituent at the N3 atom of the imidazole ring, showed the best catalytic activity...
2017: Beilstein Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28904616/mechanochemical-enzymatic-resolution-of-n-benzylated-%C3%AE-3-amino-esters
#12
Mario Pérez-Venegas, Gloria Reyes-Rangel, Adrián Neri, Jaime Escalante, Eusebio Juaristi
The use of mechanochemistry to carry out enantioselective reactions has been explored in the last ten years with excellent results. Several chiral organocatalysts and even enzymes have proved to be resistant to milling conditions, which allows for rather efficient enantioselective transformations under ball-milling conditions. The present article reports the first example of a liquid-assisted grinding (LAG) mechanochemical enzymatic resolution of racemic β(3)-amino esters employing Candida antarctica lipase B (CALB) to afford highly valuable enantioenriched N-benzylated-β(3)-amino acids in good yields...
2017: Beilstein Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28904615/an-effective-pd-nanocatalyst-in-aqueous-media-stilbene-synthesis-by-mizoroki-heck-coupling-reaction-under-microwave-irradiation
#13
Carolina S García, Paula M Uberman, Sandra E Martín
Aqueous Mizoroki-Heck coupling reactions under microwave irradiation (MW) were carried out with a colloidal Pd nanocatalyst stabilized with poly(N-vinylpyrrolidone) (PVP). Many stilbenes and novel heterostilbenes were achieved in good to excellent yields starting from aryl bromides and different olefins. The reaction was carried out in a short reaction time and with low catalyst loading, leading to high turnover frequency (TOFs of the order of 100 h(-1)). The advantages like operational simplicity, high robustness, efficiency and turnover frequency, the utilization of aqueous media and simple product work-up make this protocol a great option for stilbene syntheses by Mizoroki-Heck reaction...
2017: Beilstein Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28904614/theoretical-simulation-of-the-infrared-signature-of-mechanically-stressed-polymer-solids
#14
Matthew S Sammon, Milan Ončák, Martin K Beyer
Mechanical stress leads to deformation of strands in polymer solids, including elongation of covalent bonds and widening of bond angles, which changes the infrared spectrum. Here, the infrared spectrum of solid polymer samples exposed to mechanical stress is simulated by density functional theory calculations. Mechanical stress is described with the external force explicitly included (EFEI) method. The uneven distribution of the external stress on individual polymer strands is accounted for by a convolution of simulated spectra with a realistic force distribution...
2017: Beilstein Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28904613/a-recursive-microfluidic-platform-to-explore-the-emergence-of-chemical-evolution
#15
David Doran, Marc Rodriguez-Garcia, Rebecca Turk-MacLeod, Geoffrey J T Cooper, Leroy Cronin
We propose that a chemically agnostic approach to explore the origin of life, using an automated recursive platform based on droplet microfluidics, could be used to induce artificial chemical evolution by iterations of growth, speciation, selection, and propagation. To explore this, we set about designing an open source prototype of a fully automated evolution machine, comprising seven modules. These modules are a droplet generator, droplet transfer, passive and active size sorting, splitter, incubation chamber, reservoir, and injectors, all run together via a LabVIEW(TM) program integration system...
2017: Beilstein Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28904612/block-copolymers-from-ionic-liquids-for-the-preparation-of-thin-carbonaceous-shells
#16
Sadaf Hanif, Bernd Oschmann, Dmitri Spetter, Muhammad Nawaz Tahir, Wolfgang Tremel, Rudolf Zentel
This paper describes the controlled radical polymerization of an ionic-liquid monomer by RAFT polymerization. This allows the control over the molecular weight of ionic liquid blocks in the range of 8000 and 22000 and of the block-copolymer synthesis. In this work we focus on block copolymers with an anchor block. They can be used to control the formation of TiO2 nanoparticles, which are functionalized thereafter with a block of ionic-liquid polymer. Pyrolysis of these polymer functionalized inorganic nanoparticles leads to TiO2 nanoparticles coated with a thin carbonaceous shell...
2017: Beilstein Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28904611/oxidative-dehydrogenation-of-c-c-and-c-n-bonds-a-convenient-approach-to-access-diverse-dihydro-heteroaromatic-compounds
#17
REVIEW
Santanu Hati, Ulrike Holzgrabe, Subhabrata Sen
Nitrogen heteroarenes form an important class of compounds which can be found in natural products, synthetic drugs, building blocks etc. Among the diverse strategies that were developed for the synthesis of nitrogen heterocycles, oxidative dehydrogenation is extremely effective. This review discusses various oxidative dehydrogenation strategies of C-C and C-N bonds to generate nitrogen heteroarenes from their corresponding heterocyclic substrates. The strategies are categorized under stoichiometric and catalytic usage of reagents that facilitate such transformations...
2017: Beilstein Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28904610/correction-dynamic-behavior-of-rearranging-carbocations-implications-for-terpene-biosynthesis
#18
Stephanie R Hare, Dean J Tantillo
[This corrects the article DOI: 10.3762/bjoc.12.41.].
2017: Beilstein Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28904609/encaging-palladium-0-in-layered-double-hydroxide-a-sustainable-catalyst-for-solvent-free-and-ligand-free-heck-reaction-in-a-ball-mill
#19
Wei Shi, Jingbo Yu, Zhijiang Jiang, Qiaoling Shao, Weike Su
In this paper, the synthesis of a cheap, reusable and ligand-free Pd catalyst supported on MgAl layered double hydroxides (Pd/MgAl-LDHs) by co-precipitation and reduction methods is described. The catalyst was used in Heck reactions under high-speed ball milling (HSBM) conditions at room temperature. The effects of milling-ball size, milling-ball filling degree, reaction time, rotation speed and grinding auxiliary category, which would influence the yields of mechanochemical Heck reactions, were investigated in detail...
2017: Beilstein Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28904608/the-chemistry-and-biology-of-mycolactones
#20
REVIEW
Matthias Gehringer, Karl-Heinz Altmann
Mycolactones are a group of macrolides excreted by the human pathogen Mycobacterium ulcerans, which exhibit cytotoxic, immunosuppressive and analgesic properties. As the virulence factor of M. ulcerans, mycolactones are central to the pathogenesis of the neglected disease Buruli ulcer, a chronic and debilitating medical condition characterized by necrotic skin ulcers. Due to their complex structure and fascinating biology, mycolactones have inspired various total synthesis endeavors and structure-activity relationship studies...
2017: Beilstein Journal of Organic Chemistry
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