Neuere Ergebnisse der Azulen‐Chemie

Häfner, Klaus

doi:10.1002/ange.19580701402

Cited by 134 publications

(23 citation statements)

References 59 publications

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“…In general, aromaticity to a greater or lesser extent is expected in the following classes of organic compounds: (a) monocyclic [4 n + 2] annulenes ( n is the number of π ‐electrons) including benzenoid hydrocarbons and their substituted derivatives and fully conjugated carbocyclic (mono and poly) anions and cations containing 4 n + 2 peripheral π ‐electrons; (b) condensed conjugated carbocycles including benzenoid systems such as naphthalene and other such as azulene;9 (c) fully conjugated heterocycles (heteroaromatics) of which a vast variety exist as was pointed out earlier by Balaban;10–12 and (d) ferrocenes and related sandwich systems. Around 50% of all known organic compounds may be classified as containing aromatic ring systems.…”

Section: Introductionmentioning

confidence: 99%

Supportless Silver Nanowires as Oxygen Reduction Reaction Catalysts for Hydroxide‐Exchange Membrane Fuel Cells

Alia¹,

Duong²,

Liu³

et al. 2012

ChemSusChem

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Silver nanowires (AgNWs) and nanoparticles (AgNPs) have been synthesized to facilitate hydroxide-exchange membrane fuel cell development and commercialization. AgNWs and AgNPs with variable diameters (25-60 nm AgNWs, 2.4-30 nm AgNPs) have been studied with rotating-disk electrode experiments to examine the impact of size and morphology on the oxygen reduction reaction (ORR). Although a detrimental particle size effect is observed, AgNWs exceed the specific activity of bulk polycrystalline Ag. AgNWs with a diameter of 25 nm further exceed the ORR specific and mass activity of 2.4 nm AgNPs 5.3 times and by 16 %, respectively. Rotating ring-disk electrode testing demonstrates minimal peroxide formation on AgNWs; peroxide production increases with the use of AgNPs by as much as an order of magnitude and further increases with particle size reduction. Silver catalysts demonstrate alcohol tolerance for ORR, illustrating the benefit of silver and AgNWs as catalysts in hydroxide and alcohol hydroxide-based fuel cells.

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Section: Introductionmentioning

confidence: 99%

Supportless Silver Nanowires as Oxygen Reduction Reaction Catalysts for Hydroxide‐Exchange Membrane Fuel Cells

Alia¹,

Duong²,

Liu³

et al. 2012

ChemSusChem

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“…Owing to its unique fluorescence and ultraviolet spectral properties [1,2], the non-alternating bi-cyclic aromatic azulene has been intensively investigated for decades [3,4]. Many derivatives of azulene have been used in a variety of medicinal applications [5], nonetheless, no synthesis of an enantiomerically pure L-amino acid containing the azulene moiety has been reported, so far.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of ?-(1-azulenyl)-L-alanine as a potential blue-colored fluorescent tryptophan analog and its use in peptide synthesis

et al. 2000

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Acetyl-beta-(1-azulenyl)-D,L-alanine has been synthesized in high overall yield by the malonic ester condensation procedure, and the racemate has been enzymatically resolved with acylase I from Aspergillus melleus. The enantiomerically pure L-amino acid is of interest as a blue-colored fluorescent tryptophan analog. The bioactivity data of a heptagastrin analog containing it suggests that the planar aromatic azulene moiety may indeed mimic the tryptophan side chain to some extent, and the spectral properties of the azulene moiety makes beta-(1-azulenyl)-L-alanine of potential value as a UV and fluorescence probe in synthetic peptides, and possibly even in proteins if bioincorporation succeeds with chemically misacylated tRNAs.

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“…20,21 Thus the reaction of sodium 1,2,3-triphenylcyclopentadienide with 1-methylpyridinium iodide yields 1,2,3-triphenylazulene in 20% yield. 10 The total synthesis of 7-isopropenyl-4-methylazulene-1-carbaldehyde (lactaroviolin) has been carried out in a similar way; the first step involved treatment of 3-isopropenyl-1-methylpyridinium bromide with sodium cyclopentadienide. For example, 7-ethyl-1,4-dimethylazulene (chamuzulene) was prepared in this way from 5-ethyl1,2dimethylpyridinium bromide and sodium methylcyclopentadienide.…”

Section: N Me Mementioning

confidence: 99%

Ring Transformation of Pyridines and Benzo Derivatives under the Action of C-Nucleophiles

Gromov¹

2000

HETEROCYCLES

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The data on ring transformations of heterocyclic systems containing a pyridine ring on treatment with C-nucleophiles are generalized and described systematically over the period of up to 1999. CONTENTS I. Introduction II. Cyclopentadiene derivatives III. Ketones and enamines 1. Ring transformations of dinitropyridones 2. Ring transformations of nitropyridinium salts into indoles IV. β-Dicarbonyl compounds and carboxylic acids V. Nitroalkanes and sulfoxides VI. Conclusion I. INTRODUCTIONPyridine ring is relatively stable against cleavage, although it is less stable than benzene.The Zincke-König reaction, 1 i.e. cleavage of the quaternized pyridine ring on treatment with aromatic amines to give glutaconic dialdehyde dianils, was historically the first comprehensively studied example of this type of reaction. Subsequently, numerous ring transformations of the pyridine ring induced by nucleophiles have been discovered and studied. 2 They include, first of all, a number of new rearrangements some of which are general for the chemistry of heterocyclic compounds, such as the amidine rearrangement 3 and the enamine rearrangement of pyridine derivatives found in our study. 4 Nevertheless, no comprehensive and special review on ring transformations of the pyridine ring induced by C-nucleophiles have been published so far. Since the search for new types of ring transformations of heterocycles on treatment with Cnucleophiles remains a topical problem (see, for example, a review devoted to ring transformations of pyrimidines 5 ) and the interest of synthetic chemists in the development of original synthetic procedures based on these reactions persists, it appears pertinent to follow the development and the characteristic features of studies carried out along this line.Carbanions are species presenting considerable interest, first of all, due to the fact that they have diverse structures and functional groups and thus they are potentially capable of being incorporated according to various patterns into molecules formed in the ring transformations of the pyridine ring.Carbanions are mild nucleophiles; therefore, they mainly add to a pyridine ring at position 4 rather than 2. 6-9 The resulting 1,4-dihydropyridines cannot undergo electrocyclic cleavage of the pyridine ring because it is possibleonly for 1,2-dihydropyridine derivatives. Apparently, this fact hampers the conduction of ring transformations of pyridine derivatives induced by C-nucleophiles. This is partly responsible for the fact that only few types of reactions involving carbanions can be found in the literature and are considered below. However, the great synthetic potential of ring transformations of the pyridine ring involving C-nucleophiles makes further efforts along this line not merely justified but even highly promising. II. CYCLOPENTADIENE DERIVATIVESThe first example of ring transformation of pyridinium salts on treatment with С-nucleophiles was represented by the Ziegler-Hafner synthesis 10,11 of azulenes; one variant of this reaction makes use of pyridin...

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Neuere Ergebnisse der Azulen‐Chemie

Cited by 134 publications

References 59 publications

Supportless Silver Nanowires as Oxygen Reduction Reaction Catalysts for Hydroxide‐Exchange Membrane Fuel Cells

Supportless Silver Nanowires as Oxygen Reduction Reaction Catalysts for Hydroxide‐Exchange Membrane Fuel Cells

Synthesis of ?-(1-azulenyl)-L-alanine as a potential blue-colored fluorescent tryptophan analog and its use in peptide synthesis

Ring Transformation of Pyridines and Benzo Derivatives under the Action of C-Nucleophiles

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