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991.
Catalytic and Asymmetric Fluorolactonisations of Carboxylic Acids through Anion Phase Transfer 下载免费PDF全文
Dr. Dixit Parmar Dr. Modhu Sudan Maji Prof. Dr. Magnus Rueping 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(1):83-86
Catalytic fluorolactonisations of aromatic carboxylic acids have been developed. The reactions proceed under mild conditions using the commercially available reagent Selectfluor. A weak phase transfer of the reagent mediated by Na2CO3 allows the reaction to be conducted in non‐polar solvents. Furthermore, by the use of a catalytic amount of (DHQ)2PHAL (hydroquinine 1,4‐phthalazinediyl diether), the first asymmetric fluorolactonisation has been achieved. The corresponding isobenzofuran core can be found in many biologically active molecules. 相似文献
992.
Hydroxymethylated Phyllobilins: A Puzzling New Feature of the Dioxobilin Branch of Chlorophyll Breakdown 下载免费PDF全文
Iris Süssenbacher Dr. Bastien Christ Prof. Dr. Stefan Hörtensteiner Prof. Dr. Bernhard Kräutler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(1):87-92
Colorless nonfluorescent chlorophyll (Chl) catabolites (NCCs) are formyloxobilin‐type phyllobilins, which are considered the typical products of Chl breakdown in senescent leaves. However, in degreened leaves of some plants, dioxobilin‐type Chl catabolites (DCCs) predominate, which lack the formyl group of the NCCs, and which arise from Chl catabolites by oxidative removal of the formyl group by a P450 enzyme. Here a structural investigation of the DCCs in the methylesterase16 mutant of Arabidopsis thaliana is reported. Eight new DCCs were identified and characterized structurally. Strikingly, three of these DCCs carry stereospecifically added hydroxymethyl groups, and represent bilin‐type linear tetrapyrroles with an unprecedented modification. Indeed, DCCs show a remarkable structural parallel, otherwise, to the bilins from heme breakdown. 相似文献
993.
Determination of the Absolute Configuration of Perylene Quinone‐Derived Mycotoxins by Measurement and Calculation of Electronic Circular Dichroism Spectra and Specific Rotations 下载免费PDF全文
Prof. Dr. Joachim Podlech Dr. Stefanie C. Fleck Prof. Dr. Manfred Metzler Dr. Jochen Bürck Prof. Dr. Anne S. Ulrich 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(36):11463-11470
Altertoxins I–III, alterlosins I and II, alteichin (alterperylenol), stemphyltoxins I–IV, stemphyperylenol, stemphytriol, 7‐epi‐8‐hydroxyaltertoxin I, and 6‐epi‐stemphytriol are mycotoxins derived from perylene quinone, for which the absolute configuration was not known. Electronic circular dichroism (ECD) spectra were calculated for these compounds and compared with measured spectra of altertoxins I–III, alteichin, and stemphyltoxin III and with reported Cotton effects. Specific rotations were calculated and compared with reported specific rotations. The absolute configuration of all the toxins, except for stemphyltoxin IV, could thus be determined. The validity of the assignment was high whenever reported ECD data were available for comparison, and the validity was lower when the assignment was based only on the comparison of calculated and reported specific rotations. ECD spectra are intrinsically different for toxins with a biphenyl substructure and for toxins derived from dihydroanthracene. 相似文献
994.
Transalkylation of Higher Trifluoromethylated Fullerenes with C70: A Pathway to New Addition Patterns of C70(CF3)8 下载免费PDF全文
Nikita M. Belov Marina G. Apenova Alexey V. Rybalchenko Eugenia V. Borkovskaya Dr. Natalia S. Lukonina Dr. Alexey A. Goryunkov Dr. Ilya N. Ioffe Prof. Dr. Sergey I. Troyanov Prof. Dr. Lev N. Sidorov 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(4):1126-1133
We report three new isomers of C70(CF3)8, structurally related to p7mp‐C70(CF3)10, that are inaccessible by direct trifluoromethylation, but can be easily identified among the products of the transalkylation of higher trifluoromethylfullerenes with C70. The reported compounds are characterized by UV/Vis, 1 D and 2 D COSY 19F NMR spectroscopy, and DFT calculations. A rather unusual addition pattern is observed in p6,i‐C70(CF3)8 in which one addend is attached remotely from the others; polarization of the adjacent unsaturated bonds by the addend makes the molecule readily oxidizable. 相似文献
995.
Brandon Z. Child Dr. Santanab Giri Dr. Scott Gronert Dr. Puru Jena 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(16):4736-4745
No organic molecules with electron affinities near or above those of halogens are known. We show for the first time that aromaticity rules can be used to design molecules with electron affinities far exceeding those of halogen atoms either by tailoring the ligands of cyclopentadienyl or by multiple benzoannulations of cyclopentadienyl in conjunction with the substitution of CH groups with isoelectronic N atoms. Results based on density functional theory revealed that the electron affinities of some of these organic molecules can reach as high as 5.59 eV, thus opening the door to new class of superhalogens that contain neither a metal nor a halogen atom. 相似文献
996.
Cover Picture: Direct Catalytic Addition of Alkylnitriles to Aldehydes by Transition‐Metal/NHC Complexes (Chem. Eur. J. 48/2014) 下载免费PDF全文
997.
Highly Curved Bowl‐Shaped Fragments of Fullerenes: Synthesis,Structural Analysis,and Physical Properties 下载免费PDF全文
Min‐Kuan Chen Hsin‐Ju Hsin Dr. Tsun‐Cheng Wu Bo‐Yan Kang Yen‐Wei Lee Prof. Ming‐Yu Kuo Prof. Yao‐Ting Wu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(2):598-608
Highly curved buckybowls 3 , 4 , and 5 were synthesized from planar precursors, fluoranthenes 8 , benzo[k]fluoranthenes 10 and naphtho[1,2‐k]‐cyclopenta[cd]fluoranthenes 12 , respectively, using straightforward palladium‐catalyzed cyclization reactions. These fluoranthene‐based starting materials were easily prepared from 1,8‐bis(arylethynyl)naphthalenes 6 . Both buckybowls 3 and 4 are fragments of C60, whereas 5 is a unique subunit of C70. The curved structures were identified by X‐ray crystallography, and they are deep bowls. The maximum π‐orbital axis vector (POAV) pyramidalization angle in both 3 and 4 is 12.8°. Such a high curvature is very rarely obtained. Buckybowls 5 are less curved than the others because they have a lower density of five‐membered rings, analogous to the tube portion of C70. Cyclopentaannulation increases the bowl depths of 3 and 4 , but not the maximum POAV pyramidalization angle. Among the eight buckybowls studied herein, five form polar crystals. The bowl‐to‐bowl inversion dynamics of these buckybowls can be classified into two types; one has a planar transition structure, whereas the other has an S‐shaped transition structure. A larger longitudinal length of these buckybowls corresponds to a stronger preference for the latter. The photophysical properties of these buckybowls were examined and compared with those of C60 and C70. Buckybowls 5 have absorption bands at wavelengths greater than 450 nm, which are similar to those of C70. The chiral resolution of the mono‐substituted buckybowl 4 ac was also studied by using HPLC with a chiral column. 相似文献
998.
2,2,2‐Trifluoroacetophenone as an Organocatalyst for the Oxidation of Tertiary Amines and Azines to N‐Oxides 下载免费PDF全文
Dimitris Limnios Dr. Christoforos G. Kokotos 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(2):559-563
A cheap, mild and environmentally friendly oxidation of tertiary amines and azines to the corresponding N‐oxides is reported by using polyfluoroalkyl ketones as efficient organocatalysts. 2,2,2‐Trifluoroacetophenone was identified as the optimum catalyst for the oxidation of aliphatic tertiary amines and azines. This oxidation is chemoselective and proceeds in high‐to‐quantitative yields utilizing 10 mol % of the catalyst and H2O2 as the oxidant. 相似文献
999.
Uncatalyzed Hydroamination of Electrophilic Organometallic Alkynes: Fundamental,Theoretical, and Applied Aspects 下载免费PDF全文
Dr. Yanlan Wang Camille Latouche Dr. Amalia Rapakousiou Colin Lopez Prof Isabelle Ledoux‐Rak Dr. Jaime Ruiz Prof. Jean‐Yves Saillard Prof. Didier Astruc 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(26):8076-8088
Simple reactions of the most used functional groups allowing two molecular fragments to link under mild, sustainable conditions are among the crucial tools of molecular chemistry with multiple applications in materials science, nanomedicine, and organic synthesis as already exemplified by peptide synthesis and “click” chemistry. We are concerned with redox organometallic compounds that can potentially be used as biosensors and redox catalysts and report an uncatalyzed reaction between primary and secondary amines with organometallic electrophilic alkynes that is free of side products and fully “green”. A strategy is first proposed to synthesize alkynyl organometallic precursors upon addition of electrophilic aromatic ligands of cationic complexes followed by endo hydride abstraction. Electrophilic alkynylated cyclopentadienyl or arene ligands of Fe, Ru, and Co complexes subsequently react with amines to yield trans‐enamines that are conjugated with the organometallic group. The difference in reactivities of the various complexes is rationalized from the two‐step reaction mechanism that was elucidated through DFT calculations. Applications are illustrated by the facile reaction of ethynylcobalticenium hexafluorophosphate with aminated silica nanoparticles. Spectroscopic, nonlinear‐optical and electrochemical data, as well as DFT and TDDFT calculations, indicate a strong push–pull conjugation in these cobalticenium– and Fe– and Ru–arene–enamine complexes due to planarity or near‐planarity between the organometallic and trans‐enamine groups involving fulvalene iminium and cyclohexadienylidene iminium mesomeric forms. 相似文献
1000.
Antonio Dell'Isola Dr. Matthew M. W. McLachlan Dr. Benjamin W. Neuman Hawaa M. N. Al‐Mullah Alexander W. D. Binks Warren Elvidge Dr. Kenneth Shankland Dr. Alexander J. A. Cobb 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(37):11685-11689
An efficient synthesis of spirocyclic triazolooxazine nucleosides is described. This was achieved by the conversion of β‐D ‐psicofuranose to the corresponding azido‐derivative, followed by alkylation of the primary alcohol with a range of propargyl bromides, obtained by Sonogashira chemistry. The products of these reactions underwent 1,3‐dipolar addition smoothly to generate the protected spirocyclic adducts. These were easily deprotected to give the corresponding ribose nucleosides. The library of compounds obtained was investigated for its antiviral activity using MHV (mouse hepatitis virus) as a model wherein derivative 3 f showed the most promising activity and tolerability. 相似文献