bluuebunny/crossref_metadata_2025_split huggingface dataset:
Access to Oxoquinoline Heterocycles by N‐Heterocyclic Carbene Catalyzed Ester Activation for Selective Reaction with an Enone
Authors: Fu Zhenqian , Jiang Ke , Zhu Tingshun , Torres Jaume , Chi Yonggui Robin 
Published: May 2014

AbstractOrganocatalytic ester activation is developed for a highly selective cascade reaction between saturated esters and amino enones. The reaction involves activation of the β‐carbon atom of the ester as a key step. This method allows a single‐step access to multicyclic oxoquinoline‐type heterocycles with high enantiomeric ratios.
Double CF Bond Activation through β‐Fluorine Elimination: Nickel‐Mediated [3+2] Cycloaddition of 2‐Trifluoromethyl‐1‐alkenes with Alkynes
Authors: Ichitsuka Tomohiro , Fujita Takeshi , Arita Tomohiro , Ichikawa Junji 
Published: May 2014

AbstractThe nickel‐mediated [3+2] cycloaddition of 2‐trifluoromethyl‐1‐alkenes with alkynes afforded fluorine‐containing multi‐substituted cyclopentadienes in a regioselective manner. This reaction involves the consecutive two CF bond cleavage of a trifluoromethyl or a pentafluoroethyl group through β‐fluorine elimination.
Rhodium(II)‐Catalyzed Intramolecular Cycloisomerizations of Methylenecyclopropanes with N‐Sulfonyl 1,2,3‐Triazoles
Authors: Chen Kai , Zhu Zi‐Zhong , Zhang Yong‐Sheng , Tang Xiang‐Ying , Shi Min 
Published: May 2014

AbstractA novel rhodium(II)‐catalyzed tandem cycloisomerization of methylenecyclopropanes (MCPs) with N‐sulfonyl 1,2,3‐triazoles is disclosed. The reaction produces a series of highly functionalized polycyclic N heterocycles via a rhodium imino carbene intermediate. A distinct feature of this divergent synthesis is that different types of substrates control the reaction pathways. Moreover, several interesting transformations of these products to construct diazabicyclo[3.2.1]octane derivatives are also reported.
Luminous Butterflies: Efficient Exciton Harvesting by Benzophenone Derivatives for Full‐Color Delayed Fluorescence OLEDs
Authors: Lee Sae Youn , Yasuda Takuma , Yang Yu Seok , Zhang Qisheng , Adachi Chihaya 
Published: May 2014

AbstractButterfly‐shaped luminescent benzophenone derivatives with small energy gaps between their singlet and triplet excited states are used to achieve efficient full‐color delayed fluorescence. Organic light‐emitting diodes (OLEDs) with these benzophenone derivatives doped in the emissive layer can generate electroluminescence ranging from blue to orange–red and white, with maximum external quantum efficiencies of up to 14.3 %. Triplet excitons are efficiently harvested through delayed fluorescence channels.
Rhodium‐Catalyzed Asymmetric Arylation of β,γ‐Unsaturated α‐Ketoamides for the Construction of Nonracemic γ,γ‐Diarylcarbonyl Compounds
Authors: Wang Juanjuan , Wang Min , Cao Peng , Jiang Liyin , Chen Guihua , Liao Jian 
Published: May 2014

AbstractA highly regio‐ and enantioselective rhodium‐catalyzed 1,4‐addition of arylboronic acids to β,γ‐unsaturated α‐ketoamides using a simple new chiral sulfinylphosphine ligand is described. This transformation provides an attractive approach to construct chiral nonracemic γ,γ‐diarylsubstituted carbonyl compounds, as exemplified in the concise syntheses of sertraline and tetrahydroquinoline‐2‐carboxylamide.
Abbau von Nitridoeisen(V)‐Komplexen durch N‐N‐Kupplung in Lösung: spektroskopische und theoretische Analyse
Authors: Krahe Oliver , Bill Eckhard , Neese Frank 
Published: May 2014

AbstractKryogen abgefangene FeV‐Nitrid‐Komplexe mit Cyclam‐basierten Liganden zerfallen in bimolekularen Reaktionen und bilden dabei ausschließlich FeII‐Verbindungen. Die Charakterisierung der Ausgangsverbindungen und Produkte durch Mößbauer‐Spektroskopie, Massenspektrometrie und DFT‐Rechnungen ergab, dass die Reaktion über eine reduktive Nitrid‐Kupplung und die Freisetzung von Distickstoff verläuft (2 FeVN → FeII‐NN‐FeII → 2 FeII+N2). Der Reaktionspfad, der einer “inversen” Haber‐Bosch‐Reaktion entspricht, wurde mit Computermethoden erforscht, auch um zu klären, ob die Umsetzung katalytisch aktives FeV(N) liefern könnte. Die Ergebnisse bieten Einblick in die photolytische Spaltung von FeIII‐Aziden, die zur Erzeugung von hochvalenten Fe‐Nitriden genutzt wird.
Total Synthesis and Stereochemical Reassignment of Mandelalide A
Authors: Lei Honghui , Yan Jialei , Yu Jie , Liu Yuqing , Wang Zhuo , Xu Zhengshuang , Ye Tao 
Published: May 2014

AbstractThe total synthesis of the tunicate metabolite mandelalide A and the correction of its originally assigned stereochemistry are reported. Key features of the convergent, fully stereocontrolled route include the use of a Prins cyclization for the diastereoselective construction of the tetrahydropyran subunit, Rychnovsky–Bartlett cyclization for the preparation of the tetrahydrofuran moiety, Suzuki coupling, Horner–Wadsworth–Emmons macrocyclization, and glycosylation to append the L‐rhamnose‐derived pyranoside.
Catalytic Enantioselective Nazarov Cyclization: Construction of Vicinal All‐Carbon‐Atom Quaternary Stereocenters
Authors: Jolit Anais , Walleser Patrick M. , Yap Glenn P. A. , Tius Marcus A. 
Published: May 2014

AbstractThe diastereoselective asymmetric synthesis of vicinal all‐carbon‐atom quaternary stereocenters is a challenging problem in organic synthesis for which only few solutions have been described. A catalytic asymmetric Nazarov cyclization of fully substituted dienones that provides cyclopentenone derivatives with vicinal quaternary stereocenters in high optical purity and as single diastereoisomers is now reported.
Furan‐Based o‐Quinodimethanes by Gold‐Catalyzed Dehydrogenative Heterocyclization of 2‐(1‐Alkynyl)‐2‐alken‐1‐ones: A Modular Entry to 2,3‐Furan‐Fused Carbocycles
Authors: Zhou Liejin , Zhang Mingrui , Li Wenbo , Zhang Junliang 
Published: May 2014

AbstractA strategy for in situ generation of furan‐based ortho‐quinodimethanes (o‐QDMs) by the gold(I)‐mediated dehydrogenative heterocyclization of 2‐(1‐alkynyl)‐2‐alken‐1‐ones in the presence of pyridine N‐oxide under mild reaction conditions was developed. These in situ furan‐based o‐QDMs were trapped by electron‐deficient olefins and alkynes, thus furnishing various 2,3‐furan‐fused carbocycles in good yields with high diastereo‐ and regioselectivities.
Monobenzofused 1,4‐Azaborines: Synthesis, Characterization, and Discovery of a Unique Coordination Mode
Authors: Xu Senmiao , Haeffner Fredrik , Li Bo , Zakharov Lev N. , Liu Shih‐Yuan 
Published: May 2014

AbstractWe report the first general synthesis of boron‐substituted monobenzofused 1,4‐azaborines using ring‐closing metathesis of an enamine‐containing diene as a key synthetic strategy. As part of our investigations, we discovered that the B‐C3 moiety in a 1,4‐azaborine can serve uniquely as a η2‐L‐type ligand. This functionality is exemplified by two κ2‐N‐η2‐BC Pt complexes of a boron‐pyridyl‐substituted monobenzofused‐1,4‐azaborine. Single‐crystal X‐ray diffraction analysis of the Pt complexes shows a strong structural contribution from the iminium resonance form of the monobenzofused‐1,4‐azaborine ligand. We also demonstrate that a palladium(0) complex supported by a 1,4‐azaborine‐based phosphine ligand can catalyze hydroboration of 1‐buten‐3‐yne with unique selectivity. In view of the importance of arene–metal π‐interactions in catalytic applications, this work should open new opportunities for ligand design involving the 1,4‐azaborine motif as an arene substitute.
Total Syntheses of Hyperforin and Papuaforins A–C, and Formal Synthesis of Nemorosone through a Gold(I)‐Catalyzed Carbocyclization
Authors: Bellavance Gabriel , Barriault Louis 
Published: May 2014

AbstractThe remarkable biological activities of polyprenylated polycyclic acylphloroglucinols (PPAPs) combined with their highly decorated bicyclo[3.3.1]nonane‐2,4,9‐trione frameworks have inspired synthetic organic chemists over the last decade. The concise total syntheses of four natural products PPAPs; hyperforin and papuaforins A–C, and the formal synthesis of nemorosone are reported. Key to the realization of this strategy is the short and scalable synthesis of densely substituted PPAP scaffolds through a gold(I)‐catalyzed 6‐endo‐dig carbocyclization of cyclic enol ethers for late‐stage functionalization.
Cross‐Coupling Reactions between Stable Carbenes
Authors: Weinstein Cory M. , Martin Caleb D. , Liu Liu Leo , Bertrand Guy 
Published: May 2014

AbstractBy utilizing stable carbenes with low‐lying LUMOs, coupling with the stable nucleophilic diaminocyclopropenylidene was achieved. This reaction resulted in the formation of two new and rare examples of a bent allene as well as the isolation of the first carbene–carbene heterodimer.
Multifunctional, Defect‐Engineered Metal–Organic Frameworks with Ruthenium Centers: Sorption and Catalytic Properties
Authors: Kozachuk Olesia , Luz Ignacio , Llabrés i Xamena Francesc X. , Noei Heshmat , Kauer Max , Albada H. Bauke , Bloch Eric D. , Marler Bernd , Wang Yuemin , Muhler Martin , Fischer Roland A. 
Published: May 2014

AbstractA mixed‐linker solid‐solution approach was employed to modify the metal sites and introduce structural defects into the mixed‐valence RuII/III structural analogue of the well‐known MOF family [M3II,II(btc)2] (M=Cu, Mo, Cr, Ni, Zn; btc=benzene‐1,3,5‐tricarboxylate), with partly missing carboxylate ligators at the Ru2 paddle‐wheels. Incorporation of pyridine‐3,5‐dicarboxylate (pydc), which is the same size as btc but carries lower charge, as a second, defective linker has led to the mixed‐linker isoreticular derivatives of Ru‐MOF, which display characteristics unlike those of the defect‐free framework. Along with the creation of additional coordinatively unsaturated sites, the incorporation of pydc induces the partial reduction of ruthenium. Accordingly, the modified Ru sites are responsible for the activity of the “defective” variants in the dissociative chemisorption of CO2, the enhanced performance in CO sorption, the formation of hydride species, and the catalytic hydrogenation of olefins.
Flexible Stereoselective Functionalizations of Ketones through Umpolung with Hypervalent Iodine Reagents
Authors: Mizar Pushpak , Wirth Thomas 
Published: May 2014

AbstractThe functionalization of carbonyl compounds in the α‐position has gathered much attention as a synthetic route because of the wide biological importance of such products. Through polarity reversal, or “umpolung”, we show here that typical nucleophiles, such as oxygen, nitrogen, and even carbon nucleophiles, can be used for addition reactions after tethering them to enol ethers. Our findings allow novel retrosynthetic planning and rapid assembly of structures previously accessible only by multistep sequences.
Decay of Iron(V) Nitride Complexes By a NN Bond‐Coupling Reaction in Solution: A Combined Spectroscopic and Theoretical Analysis
Authors: Krahe Oliver , Bill Eckhard , Neese Frank 
Published: May 2014

AbstractCryogenically trapped FeV nitride complexes with cyclam‐based ligands were found to decay by bimolecular reactions, forming exclusively FeII compounds. Characterization of educts and products by Mössbauer spectroscopy, mass spectrometry, and spectroscopy‐oriented DFT calculations showed that the reaction mechanism is reductive nitride coupling and release of dinitrogen (2 FeVN→FeII‐NN‐FeII→2 FeII+N2). The reaction pathways, representing an “inverse” of the Haber–Bosch reaction, were computationally explored in detail, also to judge the feasibility of yielding catalytically competent FeV(N). Implications for the photolytic cleavage of FeIII azides used to generate high‐valent Fe nitrides are discussed.
Tuning the Self‐Assembly of Oligothiophenes on Chemical Vapor Deposition Graphene: Effect of Functional Group, Solvent, and Substrate
Authors: Sun Xiuling , Mu Youbing , Zhang Jia , Wang Xiaona , Hu Pingan , Wan Xiaobo , Guo Zongxia , Lei Shengbin 
Published: May 2014

AbstractTuning and characterizing the interfacial structure of organic semiconductors on graphene is essential for graphene‐based devices. Regulation of the supramolecular assembling structure of oligothiophenes on graphene by changing functional groups attached to the backbone of oligothiophenes is described and the assembling behavior is compared with that on the basal plane of highly oriented pyrolytic graphite. It reveals that terminal functional groups attached to the conjugated backbone of oligothiophene can entirely change the assembling structures. Significant solvent and substrate effects have also been confirmed by comparing the assembling structures of oligothiophenes deposited from tetrahydrofuran, 1,2,4‐trichlorobenzene, and octanoic acid onto graphene and graphite.
Fabrication of Predominantly Mn4+‐Doped TiO2 Nanoparticles under Equilibrium Conditions and Their Application as Visible‐Light Photocatalyts
Authors: Wang Lijie , Fan Jiajie , Cao Zetan , Zheng Yichao , Yao Zhiqiang , Shao Guosheng , Hu Junhua 
Published: May 2014

AbstractThe chemical state of a transition‐metal dopant in TiO2 can intrinsically determine the performance of the doped material in applications such as photocatalysis and photovoltaics. In this study, manganese‐doped TiO2 is fabricated by a near‐equilibrium process, in which the TiO2 precursor powder precipitates from a hydrothermally obtained transparent mother solution. The doping level and subsequent thermal treatment influence the morphology and crystallization of the TiO2 samples. FTIR spectroscopy and X‐ray photoelectron spectroscopy analyses indicate that the manganese dopant is substitutionally incorporated by replacing Ti4+ cations. The absorption band edge can be gradually shifted to 1.8 eV by increasing the nominal manganese content to 10 at %. Manganese atoms doped into the titanium lattice are associated with the dominant 4+ valence oxidation state, which introduces two curved, intermediate bands within the band gap and results in a significant enhancement in photoabsorption and the quantity of photogenerated hydroxyl radicals. Additionally, the high photocatalytic performance of manganese‐doped TiO2 is also attributed to the low oxygen content, owing to the equilibrium fabrication conditions. This work provides an important strategy to control the chemical and defect states of dopants by using an equilibrium fabrication process.
The Synthesis of Dendritic EDOT–Peptide Conjugates and their Multistimuli‐Responsive Self‐Assembly into Supramolecular Nanorods and Fibers in Water
Authors: Ahlers Patrick , Frisch Hendrik , Spitzer Daniel , Vobecka Zuzana , Vilela Filipe , Besenius Pol 
Published: May 2014

AbstractWe report the synthesis of amphiphilic dendritic EDOT–peptide conjugates and discuss their stimuli‐responsive self‐assembly into polyanionic nanorods in water. In order to expand the general concept of frustrated growth, whereby attractive supramolecular interactions within the enlarged π‐system of the hydrophobic core of a dendritic peptide are hampered by repulsive interactions in the hydrophilic periphery, we show that changes in the pH and ionic strength are both able to independently trigger the self‐assembly of the dendritic monomers into supramolecular nanorods and nanofibers. These transitions are analyzed using circular dichroism and fluorescence spectroscopic methods, and the resulting supramolecular polymers are characterized by transmission electron microscopy.
Biosynthesis of Colabomycin E, a New Manumycin‐Family Metabolite, Involves an Unusual Chain‐Length Factor
Authors: Petříčková Kateřina , Pospíšil Stanislav , Kuzma Marek , Tylová Tereza , Jágr Michal , Tomek Petr , Chroňáková Alica , Brabcová Eva , Anděra Ladislav , Krištůfek Václav , Petříček Miroslav 
Published: May 2014

AbstractColabomycin E is a new member of the manumycin‐type metabolites produced by the strain Streptomyces aureus SOK1/5‐04 and identified by genetic screening from a library of streptomycete strains. The structures of colabomycin E and accompanying congeners were resolved. The entire biosynthetic gene cluster was cloned and expressed in Streptomyces lividans. Bioinformatic analysis and mutagenic studies identified components of the biosynthetic pathway that are involved in the formation of both polyketide chains. Recombinant polyketide synthases (PKSs) assembled from the components of colabomycin E and asukamycin biosynthetic routes catalyzing the biosynthesis of “lower” carbon chains were constructed and expressed in S. aureus SOK1/5‐04 ΔcolC11–14 deletion mutant. Analysis of the metabolites produced by recombinant strains provided evidence that in both biosynthetic pathways the length of the lower carbon chain is controlled by an unusual chain‐length factor supporting biosynthesis either of a triketide in asukamycin or of a tetraketide in colabomycin E. Biological activity assays indicated that colabomycin E significantly inhibited IL‐1β release from THP‐1 cells and might thus potentially act as an anti‐inflammatory agent.
Two‐Face, Two‐Turn α‐Helix Mimetics Based on a Cross‐Acridine Scaffold: Analogues of the Bim BH3 Domain
Authors: Li Xiangqian , Wang Ziqian , Feng Yingang , Song Ting , Su Pengchen , Chen Chengbin , Chai Gaobo , Yang Ying , Zhang Zhichao 
Published: May 2014

AbstractThe design of a cross‐acridine scaffold mimicking the i, i+3, i+5, and i+7 residues distributed over a two‐face, two‐turn α‐helix is described. Docking studies and 2D 1H,15N HSQC NMR spectroscopy provide compelling evidence that compound 3 d accurately reproduces the arrangement of four hotspots in the Bim BH3 peptide to permit binding to the Mcl‐1 and Bcl‐2 proteins (Ki 0.079 and 0.056 μM, respectively). Furthermore, the hotspot mutation could also be mimicked by individual or multiple deletions of side chains on the scaffold.
Facile Synthesis of Native and Protease‐Resistant Ubiquitylated Peptides
Authors: Weller Caroline E. , Huang Wei , Chatterjee Champak 
Published: May 2014

AbstractThe reversible post‐translational modification of eukaryotic proteins by ubiquitin regulates key cellular processes including protein degradation and gene transcription. Studies of the mechanistic roles for protein ubiquitylation require quantities of homogenously modified substrates that are typically inaccessible from natural sources or by enzymatic ubiquitylation in vitro. Therefore, we developed a facile and scalable methodology for site‐specific chemical ubiquitylation. Our semisynthetic strategy utilized a temporary ligation auxiliary, 2‐(aminooxy)ethanethiol, to direct ubiquitylation to specific lysine residues in peptide substrates. Mild reductive removal of the auxiliary after ligation yielded ubiquitylated peptides with the native isopeptide linkage. Alternatively, retention of the ligation auxiliary yielded protease‐resistant analogues of ubiquitylated peptides. Importantly, our strategy was fully compatible with the presence of protein thiol groups, as demonstrated by the synthesis of peptides modified by the human small ubiquitin‐related modifier 3 protein.
High Catalytic Synergism between the Components of the Rhenium Complex@Silver Hybrid Material in Alkene Epoxidations
Authors: Indra Arindam , Greiner Mark , Gericke Axel Knop , Schlögl Robert , Avnir David , Driess Matthias 
Published: May 2014

AbstractThe immobilization of a water‐soluble rhenium complex in metallic silver matrices has resulted in a highly efficient catalyst for epoxidation, which has better epoxidation catalytic activity than the individual components. This unprecedented synergism could be obtained only by using the novel immobilization methodology, and not by using the standard adsorption process. The composite catalyst has been fully characterized (by using XRD, TEM, SEM, energy‐dispersive X‐ray spectroscopy, and atomic X‐ray mapping), and the synergism has originated as a result of the proximity of the two components. Photoemission spectroscopic studies confirm the presence of +6 and +7 oxidation states of rhenium in metallic silver in the active catalyst.
NH3 Oxidation Mechanism over Cu/SAPO‐34 Catalysts Prepared by Different Methods
Authors: Yu Tie , Wang Jun , Huang Yu , Shen Meiqing , Li Wei , Wang Jianqiang 
Published: May 2014

AbstractNH3 oxidation mechanism and its inhibition effect on the selective catalytic reduction of NOx by NH3 (NH3–SCR) reaction over two series of Cu/SAPO‐34 catalysts were studied. It was found that the different NO conversions were induced by the diverse NH3 oxidation degree. X‐ray diffraction, scanning electron microscopy, H2 temperature‐programmed reduction (H2–TPR), and CO diffuse reflectance infrared Fourier transform spectroscopy (CO–DRIFTS) analyses were conducted to estimate the Cu species distribution. The TPR results showed that the CuO species was dominant in impregnated Cu/SAPO‐34 samples, and the ion‐exchanged Cu/SAPO‐34 samples contained more isolated Cu2+ species. Furthermore, H2–TPR, electron paramagnetic resonance, and CO–DRIFTS analyses were utilized to quantify the CuO, Cu2+, and Cu+ species. The results together with the kinetic results revealed the CuO is the active site for NH3 oxidation, and the NH3 oxidation over Cu/SAPO‐34 sample consists two steps: (a) NO production; (b) further NO consumption by adsorbed NH3 species on Cu2+ sites. Finally, the inhibition of NH3 oxidation on NH3–SCR activity was explained and the NO conversion at high temperature was related to the Cu2+/CuO ratio in Cu/SAPO‐34 sample.
Poly(γ‐glutamic acid)/Silica Hybrids with Calcium Incorporated in the Silica Network by Use of a Calcium Alkoxide Precursor
Authors: Poologasundarampillai Gowsihan , Yu Bobo , Tsigkou Olga , Wang Daming , Romer Frederik , Bhakhri Vineet , Giuliani Finn , Stevens Molly M. , McPhail David S. , Smith Mark E. , Hanna John V. , Jones Julian R. 
Published: May 2014

AbstractCurrent materials used for bone regeneration are usually bioactive ceramics or glasses. Although they bond to bone, they are brittle. There is a need for new materials that can combine bioactivity with toughness and controlled biodegradation. Sol‐gel hybrids have the potential to do this through their nanoscale interpenetrating networks (IPN) of inorganic and organic components. Poly(γ‐glutamic acid) (γ‐PGA) was introduced into the sol‐gel process to produce a hybrid of γ‐PGA and bioactive silica. Calcium is an important element for bone regeneration but calcium sources that are used traditionally in the sol‐gel process, such as Ca salts, do not allow Ca incorporation into the silicate network during low‐temperature processing. The hypothesis for this study was that using calcium methoxyethoxide (CME) as the Ca source would allow Ca incorporation into the silicate component of the hybrid at room temperature. The produced hybrids would have improved mechanical properties and controlled degradation compared with hybrids of calcium chloride (CaCl2), in which the Ca is not incorporated into the silicate network. Class II hybrids, with covalent bonds between the inorganic and organic species, were synthesised by using organosilane. Calcium incorporation in both the organic and inorganic IPNs of the hybrid was improved when CME was used. This was clearly observed by using FTIR and solid‐state NMR spectroscopy, which showed ionic cross‐linking of γ‐PGA by Ca and a lower degree of condensation of the Si species compared with the hybrids made with CaCl2 as the Ca source. The ionic cross‐linking of γ‐PGA by Ca resulted in excellent compressive strength and reduced elastic modulus as measured by compressive testing and nanoindentation, respectively. All hybrids showed bioactivity as hydroxyapatite (HA) was formed after immersion in simulated body fluid (SBF).