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  • 1
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0947-3440
    Keywords: Calix[n]arenes (n = 4-13) ; Macrocycles ; Calculations, force-field ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of ten inverse calix[n]arenes (2-11) bearing four to thirteen benzene units were prepared by starting from 3,4,5-trimethoxybenzaldehyde followed by LC separation on silica gel. In 2-11 the substitution pattern is interchanged compared with the usual calixarenes. The conformational analysis was undertaken by variable temperature 1H-NMR spectroscopy and by MM2 calculations. Calix[4]arene 2 is a rigid molecule and shows the 1,3-alternate conformation which in addition was proven by X-ray analysis. At low temperatures the calix[5]arene 3 adopts the uudod conformation, where a methyl group of one benzene unit residues in the cavity of the macrocycle. At low temperature calix[6]arene 4 forms an 1:2 equilibrium between the 1,3,5-alternate (ududud; 4E) and the uududu (4B) conformation. Conformation 4B can be regarded as an intramolecular combination of a cone and an alternate arrangement of the benzene units. The calix[8]-arene shows the highest ΔG* value of the series and adopts an uuududdd conformation at low temperature. The inverse calixarenes 5 and 7-11 bearing seven and nine to thirteen aromatic units, respectively, are conformationally highly flexible systems even at low temperatures.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Condensed Ring Systems, XVI1). Synthesis, Crystal and Molecular Structure of a 1,4-Bridged Dewar-Benzene of the [6.2.2]Propellane Series with Conformational EnantiomerismStarting from 3,4:5,6-dibenzo-10,13-dithia[6.3.3]propella-3,5-diene (1) racemic 3,4:5,6-dibenzo-[6.2.2]propella-3,5,9,11-tetraene (7) is prepared. Its constitution is established by X-ray structure analysis. An enantiomeric enrichment of 7 has been achieved by chromatography on triacetyl cellulose; its halflife at 20°C is about 100 h.
    Notes: Ausgehend von 3,4:5,6-Dibenzo-10,13-dithia[6.3.3]propella-3,5-dien (1) wird das racemische 3,4:5,6-Dibenzo[6.2.2]propella-3,5,9,11-tetraen (7) hergestellt. Seine Konstitution wird röntgenstrukturanalytisch bewiesen. Durch Chromatographie an Triacetylcellulose konnte eine Anreicherung der Enantiomeren von 7 erreicht werden, deren Halbwertszeit bei 20°C ca. 100 h beträgt.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Condensed Ring Systems, XV. About the Reaction of α-Chloro Sulfoxides with Potassium tert-Butoxide by the Example of the Synthesis of OxapropellenesThe synthesis of dithia- 1a - 3a and oxathiapropellenes 1b - 3b is described. From 1b - 3b the α-chloro sulfoxides 4 - 6 and α-chloro sulfones 4a - 6a are prepared, or which in most cases several stereoisomeric racemates are obtained. The constitution, configuration, and conformation of the α-chloro sulfoxide 4, the main product obtained from 1b, was elucidated by X-ray structure analysis. Only in that way it was possible to deduce the constitutions and configurations of the other stereoisomeric α-chloro sulfoxides 4 - 6 and α-chloro sulfones 4a - 6a, respectively, using 13C NMR spectroscopy. By the reaction of the α-chloro sulfones 4a - 6a with potassium tert-butoxide (Ramberg-Bäcklund reaction) the corresponding oxapropellenes 7 - 9 are obtained only in low yields (〈 10%). Contrary, the α-chloro sulfoxides 4 - 6, und analogous conditions give yields of 80 - 90% (from 4, 6) and 25% (from 5).
    Notes: Es wird die Synthese der Dithia- 1a - 3a und Oxathiapropellene 1b - 3b beschrieben. Aus 1b - 3b werden die α-Chlorsulfoxide 4 - 6 und α-Chlorsulfone 4a - 6a hergestellt, von denen meist mehrere stereoisomere Racemate erhalten werden. Konstitution, Konfiguration und Konformation des Hauptprodukts der aus 1b erhaltenen α-Chlorsulfoxide 4 wurden durch Röntgenstrukturanalyse ermittelt. Erst dadurch wurde es möglich, mit Hilfe der 13C-NMR-Spektroskopie die Konstitutionen und Konfigurationen der anderen stereoisomeren α-Chlorsulfoxide 4 - 6 und α-Chlorsulfone 4a - 6a aufzuklären. Bei der Reaktion der α-Chlorsulfone 4a - 6a mit Kalium-tert-butylat (Ramberg-Bäcklund-Reaktion) erhält man die entsprechenden Oxapropellene 7 - 9 nur in geringer Ausbeute (〈 10%), während die α-Chlorsulfoxide 4 - 6 unter analogen Bedingungen Ausbeuten von 80 - 90% (aus 4, 6) und 25% (aus 5) ergeben.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: New Helical Molecules, IX. Syntheses, Enantiomer Separations, Circular Dichroism, Racemization Barriers, X-Ray Analyses, and Absolute Conformations of New, Easily Available ArenicenesThe new helical compounds 1-3 have been synthesized. 1 and 2 are separated into the enantiomers by chromatography on cellulose triacetate. The rotatory powers are high: e.g., [α]43620 = 2096 for 1. The racemization/ring inversion barriers range between 115 and 125 kJ/mol. X-ray analyses of 1-3 reveal different torsional angles between the rings ABC from 3.6 to 10.4°. They are compensated through the different interplanar angles of A and C with the plane B in such a way that the distance d between the intraanular C-Atoms in all compounds 1-4 is similar (2.57-2.60 Å). Correspondingly, the δ(Hi) values of 1-4 are found to differ only slightly (5.32-5.67 ppm). A determination of the absolute conformation using Bijvoets method shows (-)-2 (λ = 546 nm) to be the P-helix, and ( + )-2 the M-helix.
    Notes: Die neuen helicalen Verbindungen 1-3 werden synthetisiert, 1 und 2 durch Chromatographie an Triacetylcellulose in die Enantiomeren getrennt. Die optischen Drehungen sind hoch: z. B. [α]43620 = 2096 für 1. Die Racemisierungs-/Ringinversionsbarrieren liegen zwischen 115 und 125 kJ/mol. Röntgenstrukturanalysen von 1-3 ergeben unterschiedliche Torsionswinkel zwischen den Ringen ABC von 3.6-10.4°. Sie werden durch die unterschiedlichen Interplanarwinkel von A und C mit der Ebene B derart kompensiert, daß der Abstand d zwischen den intraanularen C-Atomen bei allen Verbindungen 1-4 nahezu gleich ist (2.57-2.60 Å). Entsprechend wird auch für δ(Hi) von 1-4 eine nur geringfügig variierende Verschiebung von 5.32-5.67 ppm gefunden. Die Bestimmung der absoluten Konformation nach der Bijvoet-Methode ergab für (-)-2 (λ = 546 nm) die P-, für ( + )-2 die M-Helix-Struktur.
    Additional Material: 2 Ill.
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  • 6
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Chemistry and Stereochemistry of Iridoids, IV. - Synthesis and X-Ray Structure Analysis of 15-Methyl-12-epi-prostaglandin F2βCrystalline(15R)- and (15S)-15-methyl-12-epi-PGF2β [15R)-5b and 5b] are synthesized enantiomerically pure starting from (1S,6R,9R)-(+)-7,9-bis(p-phenylbenzoyloxy)-3-oxabicyclo- [4.3.0]nonan-2-ol (1), which is prepared from catalpol. Contrary to our described synthesis of 12-epi-PGF2β, the intermediate products 2-5a are crystalline by virtue of the introduction of the p-phenylbenzoyl protecting group. Thus, their physical constants could be determined unequivocally. The X-ray structure analysis of (15R)-15-epi-PGF2β proves the correctness of our earlier statements based on analytical and spectroscopical investigations.
    Notes: Ausgehend von dem aus Catalpol hergestellten (1S,6R,7R,9R)-(+)-7,9-Bis(p-phenylbenzoyloxy)-3-oxabicyclo[4.3.0]nonan-2-ol (1) werden (15R)- und (15S)-15-Methyl-12-epi-PGF2β [(15R)-5b und 5b] kristallin und enantiomerenrein synthetisiert. Im Gegensatz zu der von uns beschriebenen Synthese von 12-epi-PGF2β sind durch die Einführung der p-Phenylbenzoyl-Schutzgruppen auch die Zwischenprodukte 2-5a kristallin, so daß ihre physikalischen Konstanten eindeutig bestimmt werden konnten. Die Röntgenstrukturanalyse von (15R)-15-Methyl-12-epi-PGF2β beweist, daß die von uns aus den analytischen und spektroskopischen Untersuchungen gemachten Aussagen richtig sind.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Chemistry of Ginkgolides, I. - 10-Acetyl-1-methoxycarbonyl-2,3,14,15,16-pentanorginkgolide A, an Intermediate for the Synthesis of BilobalideThe title compound 8b, an intermediate of the intended partial synthesis of bilobalide (10) is obtained by degradation of ginkgolide A (1). The X-ray structural analysis of 14,15,16-trinorginkgolide A (7) confirms the structure of the rings B - E of the ginkgolides.
    Notes: Die Titelverbindung 8b, ein Zwischenprodukt der beabsichtigten Partialsynthese von Bilobalid (10), wird durch Abbau von Ginkgolid A (1) gewonnen. Durch Röntgenstrukturanalyse von 14,15,16-Trinorginkgolid A (7) wird die Struktur der Ringe B - E der Ginkgolide bestätigt.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Natural Products from Medicinal Plants, XXIV. - Isolation, Structure Determination, and Synthesis of (Z,Z)-4,4′-(1,4-Pentadiene-1,5-diyl)diphenol, an Unusual Natural Product from the Leaves of the Ginkgo Tree (Ginkgo biloba L.)The title compound 1 was isolated from the leaves of the ginkgo tree by column chromatography. The structure of the new natural product was determined by synthesis starting from the bis(phosphorane) 3 und by X-ray analysis of its O,O′-bis(4-nitrobenzoyl) derivative 2.
    Notes: Die Titelverbindung 1 wird aus den Blättern des Ginkgo-Baumes säulenchromatographisch isoliert. Die Struktur des neuen Naturstoffs wird durch Synthese aus dem Bis(phosphoran) 3 und durch Röntgenstrukturanalyse seines O,O′-Bis(4-nitrobenzoyl)-Derivats 2 bewiesen.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Chemistry and Stereochemistry of Iridoids, IX1). - EPC Synthesis of (1R,2R,2″Z)-(-)-Methyl Jasmonate from Catalpol - Crystal and Molecular Structure of Methyl Dehydrojasmonate SemicarbazoneCatalpol is converted into the enantiomerically pure (1R,2R,2″Z)-(-)-methyl jasmonate (1) by a 16-step synthesis (yield about 7%). The R-configuration at C-1 of 1 results from the synthesis. The complete stereochemistry of 1 is confirmed by the X-ray analysis of methyl dehydrojasmonate semicarbazone (semicarbazone of 12).
    Notes: In einer 16stufigen Synthese wird aus Catalpol das enantiomerenreine (1R,2R,2″Z)-(-)-Methyl-jasmonat (1) hergestellt (Ausbeute ca. 7%). Durch die Synthese ist die R-Konfiguration an C-1 von 1 vorgegeben. Mit der Röntgenstrukturanalyse des Methyl-dehydrojasmonat-semicarbazons (Semicarbazon von 12) wird die vollständige Stereochemie von 1 bestätigt.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0170-2041
    Keywords: (-)-Coriolin ; (-)-Epicoriolin ; Radicals ; Cyclization ; Triquinans ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Radical-Type Cyclization of Dines, VI. - Total Synthesis of (-)-Coriolin and (-)-Epicoriolin from (S)-(+)-Carvone(3aR,4S,6aS)-(+)-4-(4-Methoxybenzyloxy)-6a-methyl-3,3a,4,6a-tetrahydro-2H-cyclopenta[b]furan-2-one (10) and (3aR,3bR,4R,6aS,7S,7aS)-(-)-decahydro-4,7-dihydroxy-3a,5,5-trimethyl-3-methylene-2H-cyclopenta[a]pentalen-2-one (21) are the key intermediates in the synthesis of the title compounds 1 and 1a. Enantiomerically pure 10 is produced from (S)-(+)-carvone (4) in seven straightforward reactions. Compound 21 is produced from 10 by analogy with the method developed for the synthesis of (-)-hirsutene. Through the introduction of the double bond into 21 via the silylenolether 23 one arrives at precoriolin 25, which is converted into (-)-coriolin (1) and the C-3 epimer (-)-epicoriolin (1a) (63:37) with hydrogen peroxide. The structures of 1 and 1a were confirmed via X-ray crystallography.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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