Bibliothek

feed icon rss

Ihre E-Mail wurde erfolgreich gesendet. Bitte prüfen Sie Ihren Maileingang.

Leider ist ein Fehler beim E-Mail-Versand aufgetreten. Bitte versuchen Sie es erneut.

Vorgang fortführen?

Exportieren
  • 1
    ISSN: 1434-193X
    Schlagwort(e): Thia-aza heterocycles ; Bis(azolyl)alkanes ; 1-(Haloalkyl)pyridinium halides ; Synthetic methods ; Cyclization reactions ; Ab initio calculations ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Novel 5/6/5 heterocycles, 1,3,4-thiadiazolo[3,2-a]-1,3,4-thiadiazolo[3,2-d]-1,3,5-triazinium halides 7, have been synthesized by the reaction of 2-amino-1,3,4-thiadiazoles 6 with either 1-(haloalkyl)pyridinium halides 4 or N,N′-methylenebis(pyridinium) dibromides 5. The tricyclic compounds 7 are generated in the course of several successive reaction steps in which specific proton migrations, bond-breaking and bond-forming processes occur. The structures 7 have been verified by spectral data (1H and 13C NMR, MS), X-ray analysis and ab initio calculations. The latter show that both sp2-C atoms C(10) and C(12) of 7 are significantly positively charged and, therefore, exhibit electrophilic properties towards the primary amino group of the amino-thiadiazoles 6. In the course of a multi-step reaction cascade of the 6/7 mixture, novel multi-aza/thia heterocycles 8 are formed. The structures of the latter compounds have been confirmed by X-ray analysis as well as by detailed experimental and theoretical NMR-spectroscopic studies.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 2
    ISSN: 1434-193X
    Schlagwort(e): 4-Alkylidene-1,4-dihydropyridines ; 1-Acyl-4-benzylpyridinium tetrafluoroborates ; Carboxylic acid fluorides ; X-ray structures ; Ab initio calculations ; Density functional calculations ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 1-Acyl-4-benzylpyridinium salts 4 containing nonnucleophilic anions X- such as CF3SO3-, FSO3-, and BF4- can be generated quantitatively and in situ from 1-acyl-4-alkylidene-1,4-dihydropyridines 1a-f and the corresponding acid, HX. The BF4- salts reveal an interesting and unexpected thermal instability which allows the convenient synthesis of carboxylic acid fluorides 5b-f. This procedure offers advantages over known methods: All operations can be performed in a standard glass apparatus and do not require high pressures. The formation of RCOF 5 is assisted by the pyridine moiety of 4, which splits off and functions as a Lewis base to intercept the BF3 acid. The structural and electronic relationships as well as dominating differences between the very reactive cations of 4 and their almost “inert” uncharged precursors, the dihydropyridines 1, are discussed both on the fundament of experimental evidence (X-ray structures of 1f and the extremely reactive and very labile 4f) and theoretical investigations (ab initio and DFT MO calculations).
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 3
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 1055-1064 
    ISSN: 1434-1948
    Schlagwort(e): Carbon dioxide fixation ; Magnesium ; N ligands ; C-C coupling ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of oxalic amidines R1-N=C(NHR2)-C(NHR2)=N-R1 with CH3MgX followed by uptake of CO2 results in the formation of the trimeric carbamato complexes [R1-N=C(NR2-COO)-C(NR2COO)=N-R1]3Mg3(THF)6 (2a: R1 = R2 = Ph; 2b: R1 = R2 = p-tolyl) as the thermodynamically stable final products of the reaction. Their X-ray crystal structures show that the three metal centres are in a linear arrangement. The central magnesium ion is octahedrally surrounded by six O-donor atoms of the μ2-carbamato bridges, while both peripheral magnesium ions are facially coordinated by three O-donor atoms of the carbamato groups and three THF molecules. This coordination sphere can be considered as a structural model for the active centre in the ribulose-1,5-bisphosphate carboxylase/oxygenase enzyme. Compound 2a reacts with ZnCl2 or CoBr2, with CO2 elimination, to form dimeric complexes of the type [X2M(oxalamidinato)MX2][Mg(DMF)6] (M = Zn, Co; X = Cl, Br). X-ray crystal structure analyses show that the d-metals are tetrahedrally coordinated. The magnesium-bromide-containing intermediates in the formation of 2a and 2b are able to transfer CO2 to acetophenone, thus simulating the CO2 activation step in enzymatic biotin-dependent carboxylation reactions.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 4
    ISSN: 1434-193X
    Schlagwort(e): Oxalic amidines ; Lithium diamides ; Tetraaminoethenes ; Nitrogen heterocycles ; Reduction ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Reduction of the 1,4-diaza-1,3-butadiene substructure of hexasubstituted amidines 1 with lithium metal yields the dilithium diamides 2. Subsequent reactions of these with various electrophiles give the title substances 3, 4 and 5. The quenching reaction of 2 with organosilicon derivatives leads to open-chain 3b as well as to cyclic tetraaminoethenes 4a,b. Treatment of 2 with methanol gives 3a which in the presence of oxygen is reoxidized to the starting amidine 1. Using alkyl halides as electrophiles, compounds 3c-e and 4c,d could be obtained in moderate to good yields. X-ray structural analyses of derivatives 3e and 4c reveal sterically overloaded central C-C double bonds. Whereas phosgene and its thio derivative give the imidazolines 4e,f, methyl benzoate allows a stepwise substitution leading to tetraaminoethenes bearing different residues at the nitrogen atoms.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 5
    ISSN: 1434-193X
    Schlagwort(e): 4H-Imidazoles ; Lithium-Imidazole complex ; Regioselective acylation ; Quantum-mechanical calculation ; Acyl rearrangements ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The deprotonation of the 4H-imidazoles 1 by lithium hydride yields the lithiated derivatives 2 which contain a stable delocalized anion. Surprisingly, the X-ray crystal structure analysis of 2a reveals one molecule of water in the first complexation sphere of the lithium cation. This result is in good agreement with semiempirical calculations (PM3) which predict an increase in stability on substitution of ether ligands by water molecules. The deprotonation of 1 is accompanied by a change of colour from orange to purple because of the polymethinic character of the resulting anion. Alkylation, as well as acylation, of2 leads to the exocyclic substituted derivatives 3 and 5. The NMR spectra of 3 and 5 and the semiempirical calculations suggest the existence of two rotamers due to the low rotation barrier of the exocyclic C-N bond. Another type of acylation is observed when phenylacetyl chloride is used as an acylating agent. The X-ray crystal structure analysis of 6c reveals that a rearrangement forming an unsaturated acid amide substructure takes place.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 6
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1803-1810 
    ISSN: 1434-193X
    Schlagwort(e): Oxalic amidines ; Lithium diamides ; Tetraaminoethenes ; Reduction ; Macrocycles ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A convienent one-pot synthesis of macrocycles containing a tetraaminoethene substructure is described. Starting from oxalic amidines 1, reduction with lithium and subsequent addition of phenyl isothiocyanate afforded the anionic bis(thiocarbamoyl) derivatives 3. In the final step, a ring-closure reaction using a large number of α,ω-dielectrophilic building blocks yields the new macrocyclic compounds 6-14.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 7
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1661-1668 
    ISSN: 1434-193X
    Schlagwort(e): Imidazoles ; Nucleophilic substitutions ; Fulvenes ; Pseudo-azulenes ; Heterocycles ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---The electrophilic properties of the 4H-imidazoles 1 and their protonated derivatives 2 permit the introduction of nucleophilic building blocks, as illustrated by reactions of 1 with selected amines. Depending on the nature of the amine and the substituents R1 on the heterocycle 1, single (3) or double (4) transamination is observed. The 1H-NMR spectra of the products, as well as X-ray structure analyses of compounds 3f and 4c, confirm that the residues at the 4- and/or 5-positions of 1 are exchanged. The tautomerism between 3e-h and 3e′-h′ seems to be central to the chemistry of these mixed substituted derivatives. Using orthoesters and acetophenone dimethylacetal as cyclization partners, the imidazo[4,5-d]imidazoles 5 and the 4H-imidazo[4,5-b]pyrazines 6 are obtained, respectively. Reduction of 3e with Zn/HCl or H2S leads to the air-sensitive, strongly fluorescent leuco compounds 8. Quenching of 8 by addition of aromatic aldehydes results in a condensation reaction and, coupled with the subsequent redox disproportionation, this conversion constitutes an alternative route to imidazo[4,5-d]imidazoles of type 11. The unexpected reaction of 3e-h with Lawesson's reagent allows synthesis of the 6-azapentafulvenes 14. The relevant spectral data show 14 to be members of a new chromophoric system, in which an electron-rich five-membered ring is coupled with an electron-deficient ring.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 8
    ISSN: 0947-6539
    Schlagwort(e): carbon dioxide activation ; homogeneous catalysis ; ligand effects ; molecular modeling ; rhodium ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The complexes [(P2)Rh(hfacac)] 1 [P2 = R2P-(X)-PR2] are introduced as model compounds for the investigation of the intrinsic steric properties of the [(P2)Rh] fragment. The ligand exchange processes that occur during the syntheses of 1 from [(cod)Rh(hfacac)] and the appropriate chelating diphosphanes 3 were studied by variable-temperature multinuclear NMR spectroscopy. The molecular structures of eight examples of 1 with systematic structural variations in 3 were determined by X-ray crystallography. The steric repulsion of the PR2 groups within the chelating fragment was found to significantly influence the coordination geometry of [(P2)Rh], depending on the nature and length of the backbone (X). A linear correlation between the P-Rh-P angles in the solid state and the 103Rh chemical shifts reveals a similar geometric situation in solution. A unique molecular modeling approach was developed to define the accessible molecular surface (AMS) of the rhodium center within the flexible [(P2)Rh] fragment. The potential of this model for application in homogeneous catalysis was exemplified by the use of 1 as catalysts in a test reaction, the hydrogenation of CO2 to formic acid. Complexes 1 were found to be the most active catalyst precursors for this process in organic solvents known to date.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 9
    ISSN: 0044-8249
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 10
    ISSN: 0044-8249
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
Schließen ⊗
Diese Webseite nutzt Cookies und das Analyse-Tool Matomo. Weitere Informationen finden Sie hier...