bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Novel One‐Step Approach to Synthesize Fluorescent Carbon Nanoparticles
Authors: Zhang Bing , Liu Chun‐yan , Liu Yun 
Published: August 2010

AbstractFluorescent carbon nanoparticles (CNPs) were prepared directly by a simple hydrothermal method by using L‐ascorbic acid as a carbon source. The synthesized CNPs with higher photoluminescence efficiencies (6.79 %) are monodisperse, and their diameter is about 2.0 nm. In contrast to previous methods, for this one‐step process, neither strong acid treatment nor further surface modification is necessary. Aqueous solutions of the CNPs are stable at room temperature for at least half a year. In particular, the fluorescence of the CNPs does not change over a wide pH range and even in solvents with strong ionic strengths (e.g. 2 M NaCl).
The Doubly Base‐Stabilized Diborane(4) [HB(μ‐hpp)]2 (hpp = 1,3,4,6,7,8‐hexahydro‐2H‐pyrimido[1,2‐a]pyrimidinate): Synthesis by Catalytic Dehydrogenation and Reactions with S8 and Disulfides
Authors: Schulenberg Nikola , Ciobanu Oxana , Kaifer Elisabeth , Wadepohl Hubert , Himmel Hans‐Jörg 
Published: August 2010

AbstractIn this work we report on new experiments on the catalytic dehydrogenation of [H2B(μ‐hpp)]2 leading to the doubly base‐stabilized diborane(4) [HB(μ‐hpp)]2 featuring two hpp bridges (hpp = 1,3,4,6,7,8‐hexahydro‐2H‐pyrimido[1,2‐a]pyrimidinate) under mild conditions. Several dehydrogenation (pre)catalysts were tested. The best one turned out to be Ru3(CO)12, allowing quantitative dehydrogenation already at 60 °C. Subsequently we subjected [HB(μ‐hpp)]2 to reactions with S8 and disulfides (Ph2S2 and Bn2S2, Bn = benzyl). Reaction with S8 leads to oxidative insertion of one sulfur atom into the B–B bond and formation of [HB(μ‐hpp)]2(μ‐S). In the case of disulfides, substitution reactions leading to the doubly base‐stabilized diborane(4) species [RSB(μ‐hpp)]2 and HB(μ‐hpp)2BSR (R = Ph or Bn) compete with sulfuration again leading to [HB(μ‐hpp)]2(μ‐S).
Acetylacetonato(phosphane)iridium Complexes: Synthesis and Catalytic Activity in the Cyclization of Alkynoic Acids
Authors: Geier Michael J. , Vogels Christopher M. , Decken Andreas , Westcott Stephen A. 
Published: August 2010

AbstractThe iridium complex [Ir(acac)(η2‐coe)2] (1) has been easily prepared by the addition of Tl(acac) to a suspension of [Ir(μ‐Cl)(η2‐coe)2]2 in hexane. Complex 1 has been characterized fully including an X‐ray diffraction study. It is moderately stable and is a useful precursor to a number of different acetylacetonato(phosphane)iridium complexes via addition of monodentate and bidentate phosphanes. Reactions proceeded at room temperature to give high yields of the desired square planar phosphane complexes [Ir(acac)(P)] (2: P = 2 PPh3, 3: P = 2 PMePh2, 4: P = dppm, 5: P = dppe, 6: P = dppp, 7: P = dppb, 8: P = dppf, 9: P = dcpe) except for those involving dppe, which gave a complicated mixture of products. Complex [Ir(acac)(dppe)] (5) was prepared in a microwave reactor at 125 °C. All complexes prepared in this study were efficient in the intramolecular catalyzed cyclization of4‐pentynoic acid to give exclusive formation of the exocyclic γ‐methylene‐γ‐butyrolactone. Complex 1 was found to be the most active and selective catalyst precursor for the intramolecular cyclization of both 4‐pentynoic acid and 5‐hexynoic acid.
Synthesis and Characterization of Colloidal Core–Shell Semiconductor Nanowires
Authors: Li Zhen , Ma Xuedan , Sun Qiao , Wang Zhe , Liu Jian , Zhu Zhonghua , Qiao Shi Zhang , Smith Sean C. , Lu Gaoqing (Max) , Mews Alf 
Published: August 2010

AbstractCdSe colloidal nanowires, generated from solution‐liquid‐solid approach, have been coated with CdS rods (or ribbons) by using cadmium hexadecyl xanthate (Cd‐HDX) as a single source precursor. The use of different solvents and ligands causes pronounced effects on the morphology of the nanowires. The coating process includes nucleation and growth of CdS nanorods onto the core CdSe nanowires, followed by ripening of the CdS nanorods to produce the desired core‐shell nanowire structure.
Stabilizing flaxseed oil with individual antioxidants and their mixtures
Authors: Omar Khamis Ali , Shan Liang , Wang Yan Ling , Wang Xingguo 
Published: August 2010

AbstractIn vitro reducing power tests of tea polyphenols (Tp), tert‐butylhydroquinone (TBHQ), and monoglyceride citrate (MGC) revealed that, at certain concentrations, Tp + TBHQ displayed a strong reductive capacity. Moreover, 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) radical‐scavenging activity tests showed that Tp + TBHQ was effective (p < 0.05) in quenching DPPH radicals. The effectiveness of Tp + TBHQ towards the radical‐scavenging activity was also found to be increased when their concentrations were increased. The oxidation stability of flaxseed oil (FO) was investigated as a function of time at high temperature, in the absence and presence of antioxidants; the peroxide value (PV) and p‐anisidine value of FO were determined as indicators of oxidation at 60°C during 20 days. The results revealed that Tp200 + TBHQ100 (subscripts refer to amounts in mg/kg) had noticeable reduction effects on the oxidation (PV and p‐anisidine) of FO compared with TBHQ200 regarding the PV, and when compared with the mixture of TBHQ100 + MGC100 regarding the p‐anisidine value. However, according to Rancimat tests, the ternary mixture (Tp200 + TBHQ100 + MGC100) was found to be more effective in controlling FO oxidation. The induction periods for FO containing Tp200 + TBHQ100 + MGC100, TBHQ100 + MGC100, and Tp200 + TBHQ100 were 8.305, 6.905, and 6.8020 h, respectively, whereby no significant differences were observed between TBHQ100 + MGC100 and Tp200 + TBHQ100 (p < 0.025).Practical applications: Flaxseed oil is an unstable vegetable oil due to its high content of PUFA, which are mainly composed of α‐linolenic acid (ALA). One effective way to ensure a high quality of lipids and lipid‐containing products, and to prolong their storage time, is to stabilize them by addition of suitable antioxidants. The stabilization of FO will help to increase both its shelf life and to improve its use in different applications. According to recent studies, FO contains many components that are beneficial for human health, especially ALA which can contribute to increasing the DHA and EPA content in the body. FO is believed to provide benefits in the prevention and treatment of heart diseases, arthritis, inflammatory, and autoimmune diseases.
Vinylogous Mukaiyama–Michael Reactions between 2‐Silyloxyfurans and Cyclic Enones or Unsaturated Oxo Esters
Authors: Chabaud Laurent , Jousseaume Thierry , Retailleau Pascal , Guillou Catherine 
Published: August 2010

AbstractLewis acid catalyzed vinylogous Mukaiyama–Michael (VMM) reactions between 2‐(trialkylsilyloxy)furans 1 and α,β‐unsaturated cyclic enones 2 or oxo esters 4 have been investigated. Both substrates proved to be useful Michael acceptors in the title reaction, giving the butenolides 3 and 5 in good yields. A comparative study between the α,β‐unsaturated cyclic enones 2 and the oxo esters 4 as Michael acceptors showed better diasterecontrol with the latter class of compounds. In both series, crystal structures of the major isomers revealed anti relationships of newly formed stereogenic centers. From these data, two types of transition states could be proposed: an open TS with antiperiplanar orientation or a Diels–Alder‐like TS with exo approach.
Synthesis and Reactivity of 3‐Alkynyldihydroselenophene Derivatives
Authors: Rosário Alisson R. , Schumacher Ricardo F. , Gay Bibiana M. , Menezes Paulo H. , Zeni Gilson 
Published: August 2010

AbstractWe present herein our results on the synthesis of 3‐alkynyldihydroselenophenes by palladium‐catalyzed Sonogashira cross‐coupling of 3‐iododihydroselenophenes with different alkynes under mild conditions in good to excellent yields. The developed protocol tolerated a wide range of functional groups in the dihydroselenophenes and alkynes. These 3‐alkynyldihydroselenophenes, bearing the chalcogen group, underwent highly selective intramolecular cyclizations when treated with I2to afford fused dihydroselenophene[2,3,b]selenophene rings. In addition, 3‐alkynyldihydroselenophene obtained by this methodology was also submitted to an oxidative reaction by using DDQ to give the aromatic selenophene in moderated yields.
Application of Selective Palladium‐Mediated Functionalization of the Pyrido[3′,2′:4,5]pyrrolo[1,2‐c]pyrimidine Heterocyclic System for the Total Synthesis of Variolin B and Deoxyvariolin B
Authors: Baeza Alejandro , Mendiola Javier , Burgos Carolina , Alvarez‐Builla Julio , Vaquero Juan J. 
Published: August 2010

AbstractThe reaction of protected 3‐bromo‐2‐(bromomethyl)‐4‐methoxypyrrolo[2,3‐b]pyridine and tosylmethyl isocyanide (TosMIC) afforded a pyrido[3′,2′:4,5]pyrrolo[1,2‐c]pyrimidine derivative in good yield. This compound was transformed through installation of the pyrimidine moiety in the C5 position, hydrolysis, and decarboxylation in an advanced intermediate for the total or formal synthesis of the naturalalkaloid variolin B. Reaction of 3‐bromo‐2‐(bromomethyl)‐4‐chloropyrrolo[2,3‐b]pyridine with N‐tosylmethyl dichloroformimide as a synthetic TosMIC equivalent afforded trihalo‐substituted pyrido[3′,2′:4,5]pyrrolo[1,2‐c]pyrimidine. This compound was used in a new total synthesis of the alkaloid variolin B by selective and sequential C–N, C–C, and C–O palladium‐mediated functionalization at the C9, C5, and C4 positions of the pyrido[3′,2′:4,5]pyrrolo[1,2‐c]pyrimidine system. A formal synthesis of deoxyvariolin B is also described by using the same synthetic strategy.
1‐exo‐Alkylidene‐2,3‐anhydrofuranoses: Valuable Synthons in the Preparation of Furanose‐Based Templates
Authors: Gómez Ana M. , Pedregosa Ana , Uriel Clara , Valverde Serafín , López J. Cristóbal 
Published: August 2010

AbstractHighly functionalized 1‐exo‐alkylidene‐2,3‐anhydro‐, and 1′‐halo‐1‐exo‐alkylidene‐2,3‐anhydrofuranoses can be prepared in four or five steps, respectively, from D‐mannose. These compounds feature a variety of functionalities, including a double bond, an oxirane, an allylic oxirane and (in the case of the 1′‐halo derivative) an alkenyl halide. The reactivity of each functionality in these derivatives has been explored, and the usefulness of these substrates has been demonstrated with the preparation of furanose‐based carbohydrate templates with up to four sites of molecular diversity.
Synthesis, Biological Evaluation and Docking Studies of Casuarine Analogues: Effects of Structural Modifications at Ring B on Inhibitory Activity Towards Glucoamylase
Authors: Bonaccini Claudia , Chioccioli Matteo , Parmeggiani Camilla , Cardona Francesca , Lo Re Daniele , Soldaini Gianluca , Vogel Pierre , Bello Claudia , Goti Andrea , Gratteri Paola 
Published: August 2010

AbstractWe report the total synthesis of a series of pyrrolizidine analogues of casuarine (1) and their 6‐O‐α‐glucoside derivatives. The synthetic strategy is based on a totally regio‐ and stereoselective 1,3‐dipolar cycloaddition of suitably substitutedalkenes and a carbohydrate‐based nitrone. We also report the evaluation of the biological activity of casuarine and its derivatives towards a wide range of glycosidases and a molecular modeling study focused on glucoamylase (GA) in which the binding modes of the newly synthesized compounds within the enzyme cavity are investigated. The results highlight the prominent structural features of casuarine and its derivatives that make them selective glucoamylase inhibitors.
PhI(OAc)2/KI‐Mediated Reaction of Aryl Sulfinates with Alkenes, Alkynes, and α,β‐Unsaturated Carbonyl Compounds: Synthesis of Vinyl Sulfones and β‐Iodovinyl Sulfones
Authors: Katrun Praewpan , Chiampanichayakul Supanimit , Korworapan Kanokwan , Pohmakotr Manat , Reutrakul Vichai , Jaipetch Thaworn , Kuhakarn Chutima 
Published: August 2010

Abstract(Diacetoxyiodo)benzene [PhI(OAc)2, DIB] was able to promote the reaction of sodium aryl sulfinate and potassiumiodide (KI) with alkenes and alkynes to afford the corresponding vinyl sulfones and β‐iodovinyl sulfones, respectively, in good yields. The salient features of this reaction are that it employs a commercially available and environmentally benign hypervalent iodine(III) reagent, a one‐step reaction, a short reaction time, and mild reaction conditions.
Highly Efficient and Practical Pyrrolidine–Camphor‐Derived Organocatalysts for the Direct α‐Amination of Aldehydes
Authors: Liu Pang‐Min , Magar Dhananjay R. , Chen Kwunmin 
Published: August 2010

AbstractA series of pyrrolidine–camphor‐derived organocatalysts (1–4) were designed and synthesised. These organocatalysts were used for direct α‐amination of aldehydes with dialkyl azodicarboxylates to give the desired α‐aminated products in high chemical yields (up to 92 %) and with high to excellent levels of stereoselectivity (up to >99 % ee). The reactions proceeded rapidly (within 5 min) with low catalyst loading (5 mol‐%) at ambient temperature. Enantioselective aminations of asymmetric α,α‐disubstituted aldehydes in the catalytic system were studied, with reasonable to high stereoselectivities (up to 75 % ee) being obtained. The utility of this methodology was demonstrated with the synthesis of derivatives of β‐amino‐γ‐butyrolactone and a tetrasubstitutedcyclohexane‐derived amino alcohol with high stereoselectivities. Transition models were proposed for the asymmetric α‐amination reactions; they involve hydrogen‐bond interactions between the nucleophilic enamine formed in situ and the nitrogen source.
Novel Dithienylethenes with Extended π‐Systems: Synthesis by Aldol Condensation and Photochromic Properties
Authors: Altenhöner Kai , Lamm Jan‐Hendrik , Mattay Jochen 
Published: August 2010

AbstractA facile and stereoselective route to symmetric π‐extended dithienylethene derivatives is described. The key step of this route is an aldol condensation of 1,2‐bis(5‐formyl‐2‐methylthiophen‐3‐yl)cyclopentene with a large variety of acyl compounds. All synthesized photoswitches can be reversibly converted into the closed form by irradiation with visible light. The photochromic properties of nine new dithienylethenes are discussed.
P‐Stereogenic Phosphorus Compounds: Effect of Aryl Substituents on the Oxidation of Arylmethylphenylphosphanes under Asymmetric Appel Conditions
Authors: Rajendran Kamalraj V. , Kennedy Lorna , Gilheany Declan G. 
Published: August 2010

AbstractThe effects of aryl ring substitution on the dynamic resolution of aryl(methyl)phenylphosphanes under asymmetric Appel reaction conditions have been studied. As expected, substitution at the ortho position strongly affects the degree ofstereoselection that can be achieved. Unexpectedly, however, there was no variation of stereoselectivity with the electronic nature of the para substituents, which suggests that there are two selection processes in operation. An unusual halogen‐exchange process was observed in the arylphenylphosphinous chlorides on route to the required tertiary phosphane substrates.
A Facile Synthesis of Substituted Indenones and Piperidine‐2,6‐diones from the Baylis–Hillman Acetates
Authors: Basavaiah Deevi , Lenin Dandamudi V. 
Published: August 2010

AbstractBaylis–Hillman acetates were conveniently transformed into substituted indenone and piperidine‐2,6‐dione frameworks by treatment with (di)phenylacetonitrile followed by Friedel–Crafts cyclization or imide formation.
Full Structural Characterization of an Extracellular Polysaccharide Produced by the Freshwater Cyanobacterium Oscillatoria planktothrix FP1
Authors: Silipo Alba , Molinaro Antonio , Molteni Monica , Rossetti Carlo , Parrilli Michelangelo , Lanzetta Rosa 
Published: August 2010

AbstractCyanobacteria, also known as blue‐green algae or Cyanophyta, represent one of the oldest forms of life on Earth. The organisms exhibit a high degree of biological adaptation and comprise a large group of aquatic and photosynthetic oxygenic prokaryotes that obtain their energy through photosynthesis. Cyanobacterial extracellular polysaccharides are high‐molecular‐mass hetero‐polysaccharides that are present on or released onto the cell surface and are characterized by high variability. In the present work we defined the structure of the extracellular polysaccharide produced by the freshwater cyanobacterium Oscillatoria planktothrix FP1. The structural determination, which was achieved by chemical, spectroscopic, and computational analyses, indicates a novel pentasaccharide repeating unit made up of glucose, mannose, and 2‐deoxy‐D‐ribo‐hexose, that has never previously been found in Nature. The elucidation of the structural and conformational features of the extracellular polysaccharide from Oscillatoria planktothrix is a first step toward understanding the biology of these important and interesting microorganisms.
Enantioselective One‐Pot Conjugate Addition of Grignard Reagents Followed by a Mannich Reaction
Authors: Šebesta Radovan , Bilčík Filip , Fodran Peter 
Published: August 2010

AbstractAsymmetric addition of Grignard reagents to cyclohexenone, catalyzed by ferrocene diphosphanes, afforded chiral magnesium enolates. These enolates reacted in a one‐pot arrangement with N‐benzylidenetoluenesulfonamide to give β‐amino carbonyl compounds with three contiguous stereocenters. Two major diastereoisomers (dr = 60:40) of product with enantioselectivities up to 95 % ee were separated by flash chromatography.
Isolation and Synthesis of Chivotriene, a Chivosazole Shunt Product from Sorangium cellulosum
Authors: Brodmann Tobias , Janssen Dominic , Sasse Florenz , Irschik Herbert , Jansen Rolf , Müller Rolf , Kalesse Markus 
Published: August 2010

AbstractA shunt product of chivosazole biosynthesis was isolated from the fermentation broth of Sorangium cellulosum, strain So ce 12. Its structure was elucidated by NMR spectroscopy and exhibits six chiral centers, a triene, and a labile β‐hydroxy ketone. The synthesis of chivotriene confirms the structure and in particular the proposed configuration at C22, which was originally deduced for chivosazole from the combination of its genetic and spectroscopic analyses. Remarkably, chivotriene exhibits biological activity usually not observed for segments of complex natural products. However, this activity is not connected to interference with the actin cytoskeleton, the intrinsic target of the chivosazoles.
Synthesis and Structural Analysis of Substituted Tripod‐Shaped Tri‐ and Tetra(p‐phenylene)s
Authors: Hierrezuelo Jesús , Guillén Elena , López‐Romero J. Manuel , Rico Rodrigo , López‐Ramírez M. Rosa , Otero J. Carlos , Cai Chengzhi 
Published: August 2010

AbstractWe report here the synthesis of several tripod‐shaped oligo(p‐phenylene)s with legs composed of three or four phenylene units. Each leg is end‐capped with an iodine atom or a TMS or carboxyl group, and an ethoxy group is present on the functional arm. The tripod containing methyl tri(ethylene glycol) side chains was designed for biological applications. The key step in the synthesis is the Pd‐catalyzed Suzuki cross‐coupling reaction of the silicon‐derived core molecule with the appropriately substituted p‐biphenyl moiety. This synthesis should be considered a new strategy for these compounds, as iterative coupling of the substituted p‐biphenyl building blocks with the first‐generation tripods will allow the homologation of the tripod legs to obtain giant tripod‐shaped oligo(p‐phenylene)s. Also, the iodine end‐capped leg with the ethoxy group on the functional arm permits modular design of the tripod for further functionalization, which will define the applications of the tripod‐nanostructured surfaces. The structure of some of the synthesized tripods was studied through both experimental (Raman spectra) and theoretical (DFT calculation) methods.
Verdazyl Radicals as Substrates for Organic Synthesis: Unique Access to Tetrahydropyrazolotriazinones, Pyrazolotriazinones and Dihydrotetrazinylacrylonitriles
Authors: Chen Eric K. Y. , Bancerz Matthew , Hamer Gordon K. , Georges Michael K. 
Published: August 2010

Abstract1,5‐Dimethyl‐3‐phenyl‐6‐oxoverdazyl radical was recently shown to undergo a disproportionation reaction to form an azomethine imine, which reacted with a series of dipolarophiles, to form novel tetrahydropyrazolotetrazinone heterocyclic structures, demonstrating for the first time the use of verdazyl radicals as substrates for organic synthesis. Herein, we report on the chemistry of this verdazyl radical with captodative olefins and show that the reactions that occur, either an addition reaction or a hydrogen abstraction reaction followed by a cycloaddition reaction, are defined by the captodative olefin. Also highlighted is an intramolecular rearrangement of initially formed tetrahydropyrazolotetrazinone cycloadducts to either pyrazolotriazinone or tetrahydropyrazolotriazinone structures. While the rearrangement falls under the very general definition of the Dimroth rearrangement, the mechanism that is proposed is distinct and provides the opportunity to go from one particular structural motif to another under mild conditions, expanding the usefulness of this chemistry.
Rapid Assembly of Polyfunctional Structures Using a One‐Pot Five‐ and Six‐Component Sequential Groebke–Blackburn/Ugi/Passerini Process
Authors: Al‐Tel Taleb H. , Al‐Qawasmeh Raed A. , Voelter Wolfgang 
Published: August 2010

AbstractSequential addition of up to six components under well‐defined conditions results in the formation of novel structures with amino acid, peptide, and heterocyclic components. This process forms up to eight new bonds under very mild conditions and tolerates a broad spectrum of functional groups. An orthogonal union of the Groebke–Blackburn three‐component reaction with the Ugi four‐component or Passerini three component reaction was adopted to synthesize polyfunctionalized heterocycles. In terms of diversity oriented synthesis, 10 positions on the basic polycyclic structure can be varied. Straightforward batch splitting provides a simple and efficient method for preparing structurally complex analogs.
Evidence for a Non‐Concerted, Dissoziative Mechanism of the Palladium‐Catalyzed “Enolate Claisen Rearrangement” of Allylic Esters
Authors: Braun Manfred , Meletis Panos , Schrader Wolfgang 
Published: August 2010

AbstractIn an enolate Claisen rearrangement, deprotonated allyl phenylacetate undergoes a smooth conversion at –78 °C to 2‐phenyl‐4‐pentenoic acid under palladium(0) catalysis. By using labelled starting materials in crossover experiments, the reaction is shown to follow a dissoziative, non‐concerted, non‐[3,3]‐sigmatropic mechanism that involves palladium complexes and carboxylic‐acid dianions as intermediates.
Advances towards Highly Active and Stereoselective Simple and Cheap Proline‐Based Organocatalysts
Authors: Giacalone Francesco , Gruttadauria Michelangelo , Agrigento Paola , Lo Meo Paolo , Noto Renato 
Published: August 2010

AbstractTen 4‐acyloxy‐L‐prolines were screened as catalysts at loadings of 2–0.1 mol‐% for the direct asymmetric aldol reaction in water by using variable amounts of water. Among them, a new catalyst, the L‐proline carrying a trans‐4‐(2,2‐diphenylacetoxy) group, and a catalyst previously synthesized by us, the L‐proline carrying a trans‐4‐(4‐phenylbutanoyloxy) group, were found to be excellent catalysts for the aldol reaction between cyclohexanone or cyclopentanone and substituted benzaldehydes when employed in only 1 and 0.5 mol‐%,respectively, at room temperature without additives. For such catalysts, high turnover numbers were obtained, which are among the highest values obtained for enamine organocatalysis. Finally, these catalysts can be synthesized by direct O‐acylation from inexpensive molecules and successfully used in scaled‐up reactions.