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  • 1
    Electronic Resource
    Electronic Resource
    Über Holzkohle als Adsorptionsmittel für Gase (1928)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 174 (1928), S. 142-144 
    Details
    ISSN: 0863-1786
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19281740115
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  • 2
    Electronic Resource
    Electronic Resource
    Cyclisch gekreuzt-konjugierte Bindungssysteme, 31. Das vinyloge Pentafulvalen Synthese, Zwölfelektronen-Cyclisierung, Cycloadditionen (1977)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 110 (1977), S. 1382-1402 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Cyclic Cross-Conjugated Bond Systems, 31. The Vinylogous Pentafulvalene Synthesis, Twelve-Electron Cyclisation, CycloadditionsThe synthesis of the vinylogous pentafulvalene 1 (1,2-biscyclopentadienylideneethane, 6,6′-bifulvenyl, pentafulvadiene) is described. In solution, 1 is inert towards photoexcitation but cyclizes thermally rapidly and quantitatively (Ea = 20 ± 0.4 kcal/mole, lg A = 11.3 ± 0.3; ΔH≠ = 19.4 ± 0.4 kcal/mole; ΔS≠ = -9 ± 1 e. u.) to trans-8a,8b-dihydro-as-indacene (8). The stereochemistry in 8 and consequently the conrotatory nature of this electrocyclic process  -  probable for steric reasons and with twelve participating bonding electrons symmetry-allowed  -  has been established by the vicinal coupling constants in the unsymmetrical derivatives 19 (J8,9 = 12.7 Hz) and 23 (J10,11 = 11.7 Hz) and finally by proving the C2-symmetry in the symmetrical bisadduct 21 with the help of a chiral shift reagent. 8 is photolabile and on direct excitation is cleanly isomerized back to 1. With reactive dienophiles 1 and 8 yield [4 + 2]-addition products (15-17; 19, 21); a [π2s + π10a]-type addition hoped for 8 (e. g. to 18) cannot be verified.
    Notes: Die Synthese des vinylogen Pentafulvalens 1 (1,2-Biscyclopentadienylidenethan, 6,6′-Bifulvenyl, Pentafulvadien) wird beschrieben. Es ist photochemisch inert und cyclisiert thermisch rasch und quantitativ (Ea = 20 ± 0.4 kcal/mol; lg A = 11.3 ± 0.3; ΔH≠ = 19.4 ± 0.4 kcal/mol; ΔS≠ = -9 ± 1 e. u.) zu trans-8a,8b-Dihydro-as-indacen (8). Die Stereochemie von 8 und mithin der aus sterischen Gründen ohnedies wahrscheinliche, bei Beteiligung von 12 Elektronen symmetrieerlaubte konrotatorische Verlauf dieses elektrocyclischen Prozesses wird durch Vicinalkopplungen in den unsymmetrischen Folgeprodukten 19 (J8,9 = 12.7 Hz) und 23 (J10,11 = 11.7 Hz) und letztlich durch Nachweis der C2-Symmetrie im Bisaddukt 21 mit Hilfe eines chiralen Shiftreagenzes bewiesen. 8 öffnet bei der direkten Lichtanregung einheitlich zu 1. 1 und 8 gehen mit reaktionsfähigen Dienophilen [4+2]-Addition (15-17; 19, 21) ein; eine bei 8 angestrebte [π2s + π10a]-Addition (z. B. zu 18) ist nicht erreichbar.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19771100423
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  • 3
    Electronic Resource
    Electronic Resource
    Cyclisch gekreuzt-konjugierte Bindungssysteme, 381) Vierzehn-Elektronen-Elektrocyclisierung des vinylogen Sesquifulvalens - Phenazulen (1981)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 114 (1981), S. 1697-1722 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Cyclic Cross-Conjugated Bond Systems, 381) Fourteen Electron Electrocyclisation of the Vinylogous Sesquifulvalene - PhenazuleneThe vinylogous sesquifulvalene 1 thermally undergoes 14-electron electrocyclisation with ease (Ea = 100 ± 2kj·mol-1, log A = 12.0) and perispecifically. Due to the steric constraints imposed by the system it takes place - almost certainly exclusively - in the “symmetry-forbidden”, conrotatory sense to give trans- 10a, 10b-dihydrophenazulene 2a. This is rapidly isomerized into the benzenoid 1,8- and 3,8- dihydrocyclohept[e]indenes 12/15 and is therefore not directly detectable. The trans-stereochemistry in 2a is verified by x-ray crystal analysis of its 1:1-adduct with dimethyl acetylenedicarboxylate (20). The benzylidenecyclohept[e]indenes 28a-c(obtainable from 12/15) could not be isomerised prototropically to the benzylphenazulenes 30a-c. Treatment of the cation 31 (generated from 28a) with nucleophiles also fails to produce phenazulene derivatives (34). The phenazulenium salts 38/39 are, depending on the counteranion, obtainable from 12 (15) in solution (BF-4, ClO-4) or crystalline (SbCl-6, 1/2 PtCl2-6 EE). From the BF-4 salt a deep-blue compound is generated which is stable below -60°C and in the presence of a large excess of DBN, but polymerises above 0°C or in the presence of SiO2 or Al2O3 (-60°C). It is concluded, that this blue species is phenazulene (3).
    Notes: Das vinyloge Sesquifulvalen 1 geht thermisch leicht (Ea = 100 ± 2kJ. Mol-1, log A = 12.0) und perispezifisch die 14-Elektronen-Elektrocyclisierung ein. Unter dem Zwang der Sterischen Verhältnisse erfolgt diese - sehr wahrscheinlich ausschließlich - im “symmetrieverbotenen”, konrotatorischen Sinn zum trans-10a, 10b-Dihydrophenazulen 2a. Dieses ist wegen der raschen Isomerisierung in die benzoiden 1,8- und 3,8-Dihydrocyclohept[e]indene 12/15 direkt nicht nachweisbar. Die trans-Stereochemie in 2a wird durch Röntgenstrukturanalyse seines 1:1-Addukts mit Acetylendicarbonsäure-dimethylester (20) bewiesen. Die aus 12/15 hergestellten Benzyliden-cyclohept[e]indene 28a-c konnten prototrop nicht zu den Benzylphenazulenen 30a - c isomerisiert werden. Phenazulen-Derivate (34) entstehen auch nicht bei der Umsetzung des aus 28a gewonnenen Kations 31 mit Nucleophilen. Die Phenazulenium-Salze 38/39 sind je nach Gegenion in Lösung (BF-4, CIO-4) bzw. kristallisiert aus 12 (15) herstellbar (SbCl-6, 1/2PtCl2-6). Aus dem BF-4-Salz wird eine bei -60°C und großem DBN-Überschuß beständige, tiefblaue Verbindung freigesetzt, die oberhalb 0°C bzw. im Kontakt mit SiO2O3(-60°C) rasch polymerisiert. Es wird argumentiert, daß es sich hierbei um Phenazulen (3) handelt.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19811140511
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  • 4
    Electronic Resource
    Electronic Resource
    Säureamid-Reaktionen, XXIX1) Umsetzungen von 4-Amino-uracilen mit Trisformaminomethan bzw. Formamid: Pyrimiod-pyrimidine und Dipyrimido-pyridine (1962)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 95 (1962), S. 2049-2056 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Beim Erhitzen von 4-Amino-uracilen mit Trisformaminomethan erhält man Pyrimido[4.5-d] pyrimidine. Die Umsetzung von 4-Amino-uracilen mit überschüssigem Formamid führt je nach den Reaktionsbedingungen zu Pyrimido-[4.5-d] pyrimidinen oder Dipyrimido [4.5-b: 5′.4′-e] pyridinen.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19620950828
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  • 5
    Electronic Resource
    Electronic Resource
    Ring Cleavage of Benzofurans and Tetrahydrobenzofurans by m-Chloroperbenzoic Acid Epoxidation (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 941-946 
    Details
    ISSN: 0009-2940
    Keywords: Epoxidation ; Benzofuran ; Benzofuran epoxide ; Quinone methide ; Benzofuran-2-one ; 2,4-Cyclohexadien-1-one, spiroepoxide ; cis-Ene dione ; Perester, β-hydroxy- ; 1,3-Benzodioxole ; Keto enol ester ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidation of the benzofurans 1a-f (tetrahydrobenzofurans 1g, h) with excess m-CPBA is reported. The in situ generated, highly reactive benzofuran epoxides 2a-f and their quinone methides 3a-f (cis-ene diones 3g, h) afford the labile tautomeric peroxy esters 5 and 5′ by nucleophilic addition of the peroxy acid. On elimination of m-chlorobenzoic acid, the peroxy esters 5/5′ of the benzofuran derivatives 1a-f rearrange thermally to the keto esters 6 by C—C cleavage or to the spiro epoxides 7 by C—O cleavage. The latter undergo thermal isomerization to the 1,3-benzodioxoles 8 and Diels-Alder cycloaddition to the corresponding dimers 9. Independently, the keto esters 6 and the 1,3-dioxoles 8 were synthesized by thermolysis of the dioxetanes 11. The tautomeric m-CPBA adducts 5/5′ of the persistent ene diones 3g, h, derived from the tetrahydrobenzofuran derivatives 1g, h, rearrange as well to the spiro epoxides 7g, h. In contrast to the benzofuran derivatives 6a-f, the keto enol ester 6h suffers Baeyer-Villiger rearrangement with another molecule of m-CPBA to form the ene diester 10h.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19941270523
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  • 6
    Electronic Resource
    Electronic Resource
    Thermal and Photochemical Rearrangement of 3-Substituted 2-Methylbenzofuran Epoxides and Their Valence-Isomeric Quinone Methides (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 433-436 
    Details
    ISSN: 0009-2940
    Keywords: Epoxidation ; Dioxirane, dimethyl- ; Benzofurans, 2-methyl- ; Benzofuran epoxides ; Quinone methides ; Photoisomerization ; Chromenes ; 3-Benzofuranones ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dimethyldioxirane oxidation of the 3-substituted 2-methylbenzofurans 1 [1a: 3(E)-styryl, 1b: 3-acetoxy, 1c: 3-(tert-butyldimethylsilyloxy)] is reported. Only quinone methide 3a, none of the benzofuran epoxides 2a-c, could be detected by 1H- and 13C-NMR spectroscopy at low temperature (-30°C), which on photoisomerization led to chromene 7a. The benzofuran-3-ones 5b, c and the α-diketone 6c are presumably formed by thermal isomerization of the transient benzofuran epoxides 2b, c and quinone methide 3c.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19941270220
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  • 7
    Electronic Resource
    Electronic Resource
    Preparation of 2H-Benzoxetes by Photoinduced [2 + 2] Cycloaddition of Quinone Methides, Accessible by Dimethyldioxirane (DMD) Oxidation of 2,3-Dimethylbenzofurans (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1115-1118 
    Details
    ISSN: 0009-2940
    Keywords: Epoxidation ; Dioxirane, dimethyl- ; Benzofurans, 2,3-dimethyl- ; Benzofuran epoxides ; Quinone methides ; [2 + 2] Photocycloaddition ; Benzoxetes ; Hetero-Diels-Alder reaction ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Irradiation (λ 〉 366 nm) of the quinone methides 3, which were formed by valence isomerization of the methyl-, chloro-, and tert-butyl-substituted 2,3-dimethylbenzofuran epoxides 2, afforded the novel 2H-benzoxetes 4 by photochemical [2 + 2] cycloaddition. These strained and highly labile benzoxetes 4 were spectrally (1H and 13C NMR) characterized at subambient temperatures. On prolonged storage (2-3 d) at -20 to -10°C, the benzoxetes 4 reverted to the quinone methides 3 and/or benzofuran epoxides 2.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19941270622
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  • 8
    Electronic Resource
    Electronic Resource
    Diastereoselektivität bei der Boranatreduktion von α-Triazolylketonen (1988)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 121 (1988), S. 1059-1062 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Diastereoselectivity in the Boranate Reduction of α-Triazolyl KetonesThe influence of TiCl4 on the formation of diastereomers during the boranate reduction of α-triazolyl ketones 1 is investigated. Without TiCl4 the formation of diastereomer 3 with the hydroxy and triazole goup syn to each other is preferred. However, in the presence of TiCl4 the diastereomer 2 with anti position of hydroxy and triazole group is formed with high selectivity.
    Notes: Der Einfluß von TiCl4 auf das Diastereomerenverhältnis bei der Boranatreduktin von α-Triazolylketonen 1 wird untersucht. Während ohne TiCl4 überwiegend das Diastereomere 3 mit syn-Anordnung von Triazol- und Hydroxyl-Gruppe gebildet wird, dirigiert TiCl4 die Reduktion mit hoher Selektivität zum Diastereomeren 2 mit anti-Anordnung von Triazol- und Hydroxyl-Gruppe.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19881210607
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  • 9
    Electronic Resource
    Electronic Resource
    Epoxidation of 2,3-Dimethylbenzofurans by Dimethyldioxirane (1992)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 125 (1992), S. 231-234 
    Details
    ISSN: 0009-2940
    Keywords: Epoxidation ; Dioxirane, dimethyl ; Benzofurans, 2,3-dimethyl- ; Benzofuran epoxides ; Quinone methides ; Methanol addition ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of epoxides 2 by the reaction of the chloro- and methyl-substituted 2,3-dimethylbenzofurans 1 with dimethyl-dioxirane at low temperature is reported. These labile epoxides were spectroscopically characterized (1H and 13C NMR) at subambient temperatures. Epoxidation of benzofuran 1c affords a 31:69 mixture of epoxide 2c and quinone methide 3c, the latter presumably being produced by valence isomerization of the epoxide. On warming up above -10°C, the epoxides 2 suffer decomposition. Treatment of epoxide 21 with methanol yields the tautomeric mixture of adducts 4i and 4i′.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19921250136
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  • 10
    Electronic Resource
    Electronic Resource
    Photochemical and Thermal Rearrangement of Acyl-Substituted Quinone Methides, Accessible by Dimethyldioxirane Oxidation of Benzofurans and Subsequent Valence Isomerization of the Resulting Epoxides (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 2697-2699 
    Details
    ISSN: 0009-2940
    Keywords: Epoxidation ; Dioxirane, dimethyl- ; Benzofurans, 2-methyl-3-phenyl ; Benzofuran epoxides ; Quinone methides ; (Z/E) Photoisomerization ; Norcaradiene ; Benzocycloheptafuran ; Thermal rearrangement ; Xanthenes, 9-acetyl- ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photoisomerization of quinone methides 3 to benzocycloheptafuran 4 and the thermolysis of the latter to xanthenes 5 are reported. The quinone methides 3 are accessible by dimethyldioxirane oxidation and subsequent valence isomerization of the resulting benzofuran epoxides 2. On irradiation (λ 〉 400 nm), the quinone methides 3 rearrange by cyclization to the corresponding norcaradiene, and ring enlargement affords the benzocycloheptafurans 4. Thermolysis of the cycloheptatrienes 4 leads to the xanthenes 5, first by cycloreversion to the norcaradienes, followed by electrocyclization to the chromenes and tautomerization of the latter. The new cycloheptatrienes 4 and xanthenes 5 were fully characterized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931261220
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