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Angewandte Chemie

Tim N Gieshoff, Uttam Chakraborty, Matteo Villa, Axel Jacobi von Wangelin
The replacement of noble metal technologies and the realization of new reactivities with earth-abundant metals is at the heart of sustainable synthesis. Alkene hydrogenations have so far been most effectively performed by noble metal catalysts. This study reports an iron-catalyzed hydrogenation protocol for tri- and tetra-substituted alkenes of unprecedented activity and scope under mild conditions (1-4 bar H2 , 20 °C). Instructive snapshots at the interface of homogeneous and heterogeneous iron catalysis were recorded by the isolation of novel Fe nanocluster architectures that act as catalyst reservoirs and soluble seeds of particle growth...
February 24, 2017: Angewandte Chemie
Yi Zhang, Qing Liao, Xinguo Wang, Jiannian Yao, Hongbing Fu
Development of nanowire photonics requires integration of different nanowire components into highly ordered functional heterostructures. Herein, we report a sequential self-assembly of binary molecular components into branched nanowire heterostructures (BNHs) via lattice-matched epitaxial growth, in which the microribbon backbone of 2,5-Bis(5-tert-butyl-2-benzoxazolyl)thiophene (BBOT) functions as blue-emitting microlaser source to pump the nanowire branches of BODIPY. By constructing Au electrodes on both branch sides and measuring the photocurrent in them, we successfully realize the integration of an organic laser and a power meter in a single device...
February 24, 2017: Angewandte Chemie
Ángel L Fuentes de Arriba, Elena Lenci, Mahendra Sonawane, Odilon Formery, Darren J Dixon
A new iridium-catalyzed reductive Strecker reaction for the direct and efficient formation of α-amino nitrile products from a broad range of (hetero)aromatic and aliphatic tertiary amides, and N-alkyl lactams is reported. The protocol exploits the mild and highly chemoselective reduction of the amide and lactam functionalities using IrCl(CO)[P(C6 H5 )3 ]2 (Vaska's complex) in the presence of tetramethyldisiloxane, as a reductant, to directly generate hemiaminal species able to undergo substitution by cyanide upon treatment with TMSCN (TMS=trimethylsilyl)...
February 24, 2017: Angewandte Chemie
Nurbey Gulia, Olafs Daugulis
We have developed a method for palladium-catalyzed, pyrazole-directed sp(3) C-H bond arylation by aryl iodides. The reaction employs a Pd(OAc)2 catalyst at 5-10 mol % loading and silver(I) oxide as a halide-removal agent, and it proceeds in acetic acid or acetic acid/hexafluoroisopropanol solvent. Ozonolysis of the pyrazole moiety affords pharmaceutically important β-phenethylamines.
February 24, 2017: Angewandte Chemie
Stephan M Rummelt, Gui-Juan Cheng, Puneet Gupta, Walter Thiel, Alois Fürstner
The recognition of the dual binding mode of propargyl and allyl alcohols to [Cp*Ru] fragments fostered the development of a highly regioselective intermolecular Alder-ene-type reaction of alkynes with 1,2-disubstituted alkenes. The increased substrate scope opens new perspectives in stereochemical terms. As the loaded catalyst is chiral-at-metal, stereochemical information is efficiently relayed from the propargylic site to the emerging C-C bond. This interpretation is based on the X-ray structure of the first Cp*Ru complex carrying an intact enyne ligand, and provides valuable insights into bonding and activation of the substrates...
February 23, 2017: Angewandte Chemie
Wujun Jian, Liang Ge, Yihang Jiao, Bo Qian, Hongli Bao
Because of the lack of effective alkylating reagents, alkyl etherification of olefins with general alkyl groups has not been previously reported. In this work, a variety of alkyl diacyl peroxides and peresters generated from aliphatic acids have been found to enable the first iron-catalyzed alkyl etherification of olefins with general alkyl groups. Primary, secondary and tertiary aliphatic acids are suitable for this reaction, delivering products with yields up to 97 %. Primary and secondary alcohols react well, affording products in up to 91 % yield...
February 23, 2017: Angewandte Chemie
Dilip V Patil, Seung Woo Kim, Quynh H Nguyen, Hanbyul Kim, Shan Wang, Tuan Hoang, Seunghoon Shin
A non-metal approach for accessing α-oxo carbene surrogates for a C-C bond-forming bimolecular coupling between ynamides and nucleophilic arenes was developed. This acid-catalyzed coupling features mild temperature, which is critical for the required temporal chemoselectivity among nucleophiles. The scope of nucleophiles includes indoles, pyrroles, anilines, phenols and silyl enolethers. Furthermore, a direct test of SN 2' mechanism has been provided by employing chiral N,N'-dioxides which also enlightens the nature of the intermediates in related metal-catalyzed processes...
February 23, 2017: Angewandte Chemie
Erin E Stache, Tomislav Rovis, Abigail G Doyle
The enantioselective desymmetrization of cyclic meso-anhydrides with benzyl trifluoroborates under nickel-photoredox catalysis is described. The reaction tolerates a variety of sterically and electronically different trifluoroborates, as well as structurally unique cyclic anhydrides. The trans isomer of the keto-acid products is also observed at varying levels dependent on the trifluoroborate identity and relative catalyst loading. A mechanism involving decarbonylation and Ni-C bond homolysis of a Ni(II) adduct is proposed...
February 23, 2017: Angewandte Chemie
(no author information available yet)
No abstract text is available yet for this article.
February 23, 2017: Angewandte Chemie
David E Chavez, Damon A Parrish, Lauren Mitchell, Greg H Imler
This study presents the synthesis and characterization of the oxidation products of 3,6-diazido-1,2,4,5-tetrazine (1) and 6-amino-[1,5-b]tetrazolo-1,2,4,5-tetrazine (2). 3,6-Diazido-1,2,4,5-tetrazine-1,4-dioxide was produced from oxidation with peroxytrifluoroacetic acid, and more effectively using hypofluorous acid, and 2 can be oxidized to two different products, 6-amino-[1,5-b]tetrazolo-1,2,4,5-tetrazine mono-N-oxide and di-N-oxide. These N-oxide compounds display promising performance properties as energetic materials...
February 23, 2017: Angewandte Chemie
Elena Pérez-Gallent, Marta C Figueiredo, Federico Calle-Vallejo, Marc T M Koper
Carbon dioxide and carbon monoxide can be electrochemically reduced to useful products such as ethylene and ethanol on copper electrocatalysts. The process is yet to be optimized and the exact mechanism and the corresponding reaction intermediates are under debate or unknown. In particular, it has been hypothesized that the C-C bond formation proceeds via CO dimerization and further hydrogenation. Although computational support for this hypothesis exists, direct experimental evidence has been elusive. In this work, we detect a hydrogenated dimer intermediate (OCCOH) using Fourier transform infrared spectroscopy at low overpotentials in LiOH solutions...
February 23, 2017: Angewandte Chemie
Lingying Leng, Xiaohan Zhou, Qi Liao, Falu Wang, Hao Song, Dan Zhang, Xiao-Yu Liu, Yong Qin
The asymmetric total syntheses of a group of structurally complex Kopsia alkaloids, (-)-kopsine, (-)-isokopsine, (+)-methyl chanofruticosinate, (-)-fruticosine, and (-)-kopsanone, has been achieved. The key strategies for the construction of the molecular complexity in the targets included an asymmetric Tsuji-Trost rearrangement to set the first quaternary carbon center at C20, an intramolecular cyclopropanation by diazo decomposition to install the second and third quaternary carbon centers at C2 and C7, respectively, and a SmI2 -promoted acyloin condensation to assemble the isokopsine core...
February 23, 2017: Angewandte Chemie
Bijandra Kumar, Veerendra Atla, J Patrick Brian, Sudesh Kumari, Tu Quang Nguyen, Mahendra Sunkara, Joshua M Spurgeon
Electrochemical conversion of CO2 into energy-dense liquids, such as formic acid, is desirable as a hydrogen carrier and a chemical feedstock. SnOx is one of the few catalysts that reduce CO2 into formic acid with high selectivity but at high overpotential and low current density. We show that an electrochemically reduced SnO2 porous nanowire catalyst (Sn-pNWs) with a high density of grain boundaries (GBs) exhibits an energy conversion efficiency of CO2 -into-HCOOH higher than analogous catalysts. HCOOH formation begins at lower overpotential (350 mV) and reaches a steady Faradaic efficiency of ca...
February 23, 2017: Angewandte Chemie
Javix Thomas, Nathan A Seifert, Wolfgang Jäger, Yunjie Xu
Rotational spectra of the three most stable conformers (I, II, III) of the ternary 2,2,2-trifluoroethanol (TFE) cluster were measured using Fourier transform microwave spectrometers, and unambiguously assigned with the aid of ab initio calculations. The most stable conformer, I, contains one trans-TFE subunit which is unstable in its isolated gas phase form. The study offers new insights into how the trans conformation is stabilized in TFE clusters of increasing size, and eventually becomes a dominant conformation in the liquid phase...
February 23, 2017: Angewandte Chemie
Julius F Kögel, Davor Margetić, Xiulan Xie, Lars H Finger, Jörg Sundermeyer
Herein we present the first superbase MHPN with two interacting P-ylide entities. Unlike classical proton sponges, this novel compound class has carbon atoms as basicity centers which are forced into close proximity by a naphthalene scaffold. The bisylide exhibits an experimental pKBH(+)  value of 33.3±0.2 on the MeCN scale and a calculated gas-phase proton affinity of 277.9 kcal mol(-1) (M062X/6-311+G**//M062X/6-31G*+ZPVE method) exceeding that of the corresponding monoylide by nearly 15 kcal mol(-1) ...
February 23, 2017: Angewandte Chemie
Weichun Zhang, Martín Caldarola, Biswajit Pradhan, Michel Orrit
Redox reactions are central to energy conversion and life metabolism. Herein we present electrochemical measurements with fluorescent readout of the redox-sensitive dye Methylene Blue (MB), at the single-molecule (SM) level. To overcome the low fluorescence quantum yield of MB we enhanced fluorescence by using individual gold nanorods to achieve the required sensitivity. By measuring the same molecule at different electrochemical potentials we determined the mid-point potential of each single molecule through its redox-induced fluorescence blinking dynamics...
February 23, 2017: Angewandte Chemie
(no author information available yet)
No abstract text is available yet for this article.
February 22, 2017: Angewandte Chemie
Xin Yan, Heyong Cheng, Richard N Zare
Many important chemical transformations occur in two-phase reactions, which are widely used in chemical, pharmaceutical, and polymer manufacturing. We present an efficient method for performing two-phase reactions in microdroplets sheared by sheath gas without using a phase-transfer catalyst. This avoids disadvantages such as thermal instability, high cost, and, especially, the need to separate and recycle the catalysts. We show that various alcohols can be oxidized to the corresponding aldehydes and ketones within milliseconds in moderate to good yields (50-75 %)...
February 22, 2017: Angewandte Chemie
Hiu C Lam, Henry P Pepper, Christopher J Sumby, Jonathan H George
A five-step total synthesis of (±)-verrubenzospirolactone has been achieved using a biomimetic, intramolecular Diels-Alder reaction of a 2H-chromene to form two rings and four stereocenters in the final step. This Diels-Alder reaction occurs spontaneously at 30 °C "on-water", and thus suggests that it is likely to be non-enzymatic in nature. The structure of (±)-verrubenzospirolactone was also used to inspire a quadruple cascade reaction to generate seven stereocenters, four rings, three C-C bonds, and two C-O bonds in one step...
February 22, 2017: Angewandte Chemie
Jonathan Pettinger, Yann-Vaï Le Bihan, Marcella Widya, Rob L M van Montfort, Keith Jones, Matthew D Cheeseman
The stress-inducible molecular chaperone, HSP72, is an important therapeutic target in oncology, but inhibiting this protein with small molecules has proven particularly challenging. Validating HSP72 inhibitors in cells is difficult owing to competition with the high affinity and abundance of its endogenous nucleotide substrates. We hypothesized this could be overcome using a cysteine-targeted irreversible inhibitor. Using rational design, we adapted a validated 8-N-benzyladenosine ligand for covalent bond formation and confirmed targeted irreversible inhibition...
February 22, 2017: Angewandte Chemie
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