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  • 1
    ISSN: 0947-3440
    Keywords: Diels - Alder reactions, kinetics of ; Dienophiles, relative reactivities ; Cycloadditions ; Synchronous, nonsynchronous mechanism ; Diradical-type intermediate ; Zwitterion-type intermediate ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several new 2-substituted 2-cyclopropylideneacetates 1a-X (X=F, N3, SPh, OTBDMS, OTBDPS) have been prepared. Their cycloadditions and those of some previously described compounds of type 1a-X (X=H, Br, Cl) with furan (5) and/or 6,6-dimethylfulvene (7) are reported. Several of these peculiar acrylates 1a-X (X=H, Br, Cl, F, N3), as well as allenecarboxylate 1b, regular acrylate 1c, crotonate 1d, and 3,3-disubstituted acrylates 1e-X (X=H, Cl), were reacted with furan (5) and 6,6-dimethylfulvene (7) in two series of competition experiments at 64°C. The [2 + 4] cycloaddition of 1a-Cl and 1a-Br to furan (5) are both about 16 times as fast and to dimethylfulvene (7) 230 and 210 times as fast as that of the parent acrylate 1c, while allenecarboxylate 1b reacts with 4 only 30 times as fast as 1c, and the 3-substituted acrylates 1d and 1a-X (X=H, Cl) were all too sluggish to react under these conditions. The kinetic data obtained for the cycloadditions of 1a-X suggest a mechanism involving either diradicals or zwitterions as intermediates.
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  • 2
    ISSN: 0947-3440
    Keywords: Conjugation ; X-ray diffraction ; Molecular structures ; Ab initio calculations ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Low temperature crystal structural studies of small cyclopropyl-conjugated unsaturated hydrocarbons reveal significant differences in bond lengths between carbon atoms mainly within the three-membered rings but also for adjacent C—C single bonds. The strongest influence of conjugation was observed for spiro[2.4]hepta-4,6-diene (1), where the difference in the lengths of three-membered ring bonds is 0.050 Å (X-ray). The same effect is also obvious from ab initio calculations at HF/6-31G(d) (to a minor extent) and MP2/6-31G(d) levels, as shown by a difference analysis of bond lengths which was performed in order to cancel out systematic errors and differences for both methods. Static difference electron density maps were derived from the experimental data by multipole refinements. These maps showed shifts of electron density to exocyclic locations within the planes of the three-membered rings and significant bond ellipticities for the adjacent single bonds. For 1,1-diethenylcyclopropane (4) a nonsymmetric conformation was found in the crystal lattice, very close to the global minimum structure calculated by ab initio methods.
    Additional Material: 7 Ill.
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  • 3
    ISSN: 0947-6539
    Keywords: alkynes ; coupling reactions ; cyclopropanes ; macrocycles ; oligoalkadiynes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general approach to the family of completely spirocyclopropanated macrocyclic polydiacetylenes, that is, cyclic dehydrooligomers of 1,1-diethynylcyclopropane 4, is reported. The characterized examples of these “exploding” [n]rotanes are for n = 5, 6, 7, 8, 9, 10, and 12. X-ray crystal structure analyses for the hydrocarbons with n = 5, 6, 7, and 8 disclose a strong electronic interaction between the cyclopropane and the acetylene units leading to a significant shortening of the distal and lengthening of the proximal cyclopropane bonds. While the five-sided compound 18 can occur as a planar or envelope-shaped molecule, depending on the solvent from which crystals are grown, the six- (19), seven- (20), and eight-sided (21) molecules all have chair conformations. While the butadiyne units in 18 and 19 are bent slightly outwards, those in the seven- and eight-sided molecules 20 and 21, respectively, are bent distinctly inward. All these compounds are extremely high-energy molecules: when struck with a spatula or a pestle, they go off with a puff to yield black soot.
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  • 4
    ISSN: 0947-6539
    Keywords: alkynes ; asymmetric syntheses ; cyclopropanes ; spiro compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A variety of chiral, nonracemic 2-alkoxy-1-alkynylcyclopropanes 7 were synthesized in good to very good yields from enantiomerically pure glycidol derivatives (glycidol tosylate, epichlorohydrin) by boron trifluoride promoted addition of lithium trimethylsilylacetylide followed by protection of the secondary hydroxyl group and finally a diastereoselective γ-elimination. The 2-ethoxy derivative (S,R)-7 b was deprotonated with n-butyllithium, and the resulting 1-lithio-2-ethoxy derivative (S,R)-20 functionalized by treatment with oxygen followed by tosyl chloride. Protodesilylation and catalytic hydrogenation smoothly furnished 1-ethenylcyclopropyl sulfonates, which underwent a clean Pd0-catalyzed SN2′-type substitution with dimethyl propargylsodiummalonate to give the (E)-configurated enyne (R,E)-26 with a methylenecyclopropane end group. A diastereoselective Pauson-Khand reaction completed the sequence to give the enantiomerically pure spirocyclopropaneannelated bicyclo[3.3.0]octane derivative 31.
    Additional Material: 3 Tab.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 107 (1974), S. 1702-1713 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Dispiro[2.0.2.4]deca-7,9-diene and Spiro[2.5]octa-4,6-diene: Their Chemical Reactions, Thermal and Photochemical RearrangementsSome [4 + 2]cycloaddition reactions of the title compounds 1 and 2 have been investigated. In all cases normal addition onto the 1,3-diene system is observed. 1 in the presence of proton acids at elevated temperatures yields o-ethylstyrene (16) and derivatives of 2-(o-ethylphenyl)ethane. The thermolysis of 1 above 120°C gives a mixture of 16 and tetraline (20). Higher temperatures are required for the thermal rearrangement of 2 to ethylbenzene. photo-chemically 1 yields a mixture of 16 and 20 in a ratio of about 2:1 both on direct and sensitized excitation. Possible mechanisms for these rearrangements are discussed.
    Notes: Einige [4 + 2]-Cycloadditionen der Titelverbindungen 1 und 2 werden untersucht; in allen Fällen beobachtet man normale Addition an das 1,3-Diensystem. Mit Säuren liefert 1 bei erhöhter Temperatur unter Öffnung beider Cyclopropanringe o-Äthylstyrol (16) und Derivate des 2-(o-Äthlphenyl)äthans. Die Thermolyse von 1 oberhalb 120°C führt zu 16 und Tetralin (20). Die thermische Umlagerung von 2 zu Äthylbenzol erfordert höhere Temperaturen. Photochemisch bilden sich aus 1 sowohl bei direkter als auch bei sensibilisierter Anregung 16 und 20 im Verhältnis von ca. 2:1. Mögliche Mechanismen dieser Umlagerungen werden diskutiert.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 110 (1977), S. 2561-2573 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthesis, Chemical Properties and Thermal Rearrangement of Spiro[3,4]octa-5,7-dieneThe synthesis of spiro[3.4]octa-5,7-diene (2) was achieved along two routes starting from spiro-[3.4]octan-5-one (5). In both cases the last step was a dehydrohalogenation of the halospiro-[3.4]octenes 8b/9b and 11, respectively, which had to be carried out at room temperature, because 2 dimerizes about as fast as cyclopentadiene. It also underwent addition of maleic anhydride and 2-chloroacryloyl chloride to yield 13 and 14a respectively. 14a could be degraded to the bicyclo[2.2.1]hept-2-en-5-on-7-spirocyclobutane (15a), which served as a precursor to the hydrocarbon 17. Above 90°C 2 isomerizes to a mixture of bicyclo[3.3.0]octadienes 18a and 18b. This reaction followed a first order kinetics in the gas phase with the Arrhenius equation ln(k) = 31.7 - 29200/RT. These kinetic parameters are interpreted in terms of a sigmatropic [1,5]-alkyl shift.
    Notes: Die Synthese von Spiro[3.4]octa-5,7-dien (2) gelingt ausgehend von Spiro[3.4]octan-5-on (5) auf zwei Wegen. Bei beiden wird in der letzten Stufe eine Dehydrohalogenierung eines Halogenspiro[3.4]octens 8b/9b bzw. 11 bei Raumtemperatur vorgenommen, weil 2 bei höheren Temperaturen ähnlich schnell dimerisiert wie 1,3-Cyclopentadien. Ebenso addiert es leicht Maleinsäureanhydrid und 2-Chloracryloylchlorid zu 13 bzw. 14a. 14a läßt sich zum Bicyclo[2.2.1]hept-2-en-5-on-7-spirocyclobutan (15a) abbauen, aus dem der Kohlenwasserstoff 17 zugänglich ist. Oberhalb von 90°C isomerisiert 2 zu einem Gemisch der Bicyclo[3.3.0]octadiene 18a und 18b. Die Kinetik dieser Reaktion in der Gasphase zeigt einen Verlauf erster Ordnung und folgt dem Arrhenius-Ansatz ln(k) = 31.7 - 29200/RT. Daraus ist für den Mechanismus auf eine konzertierte [1,5]-Alkylverschiebung zu schließen.
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  • 7
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Diademane and Structurally Related Compounds, I Preparation and Characteristic Reactions of Some Tris-σ-homobenzene HydrocarbonsDiademane (5) and 1,6-Homodiademane (6) are the first hydrocarbons with cis-tris-σ-homobenzene skeletons. They were prepared by photoisomerization of the olefinic precursors 8 („snoutene“) and 15 („4,5-homosnoutene“), respectively. In an analogous reaction the bridged trans-tris-σ-homobenzene 7 was formed from 17 („endo,exo-bishomobarrelene“). 7 is more easily obtained from 17 by rhodium(I)-catalyzed isomerization or from exo,exo-bishomobarrelene 18 by thermal rearrangement. The unbridged 4 was prepared using a newly developed synthetic sequence starting from 1,3-cyclohexadiene. The thermal rearrangement of 5 and 6 to triquinacene (9) and 1,10-homotriquinacene (16) is very facile; the gas phase kinetic parameters (ln k (5) = 33.7 - 31600/RT and ln k (6) = 32.2 - 28300/RT, both first order) strongly corroborate, that these rearrangements are concerted [σ2a + σ2a + σ2s]-Cycloreversions. [3,6-12C2]-labelled 4 upon thermolysis yields a trans-bicyclo[4.3.0]nona-3,7-diene (31 ≙ 22) with a 12C-labelling pattern, which proves its formation via a 3-step mechanism. The first step in this sequence most probably is a [σ2s + σ2s + σ2a] cycloreversion with ln k = 30.8 - 42000 RT(first order). Only the bridged compound 7 does not follow the same path, probably due to excessive ring strain in the transition state, and prefers a stepwise [2 + 2] cycloreversion leading to 18 and at least 5 secondary products.
    Notes: Diademan (5) und 1,6-Homodiademan (6), die ersten Kohlenwasserstoffe mit cis-Tris-σ-homo-benzol-Gerüst, wurden durch Photoisomerisierung der monoolefinischen Vorstufen 8 („Snouten“) bzw. 15 („4,5-Homosnouten“) gewonnen. Analog entstand aus 17 („endo,exo-Bis-homobarrelen“) das überbrückte trans-Tris-σ-homobenzol 7, das sich bequemer auch durch Rhodium(I)-katalysierte Isomerisierung von 17, oder thermische Umlagerung von exo,exo-Bishomobarrelen 18 erhalten ließ. Das nicht überbrückte 4 wurde nach einer neuen Synthesesequenz aus 1,3-Cyclohexadien dargestellt. Thermisch lagern sich 5 und 6 sehr leicht in Triquinacen (9) bzw. 1,10-Homotriquinacen (16) um, die gasphasen-kinetischen Parameter (In k (5) = 33.7 - 31600/RT und in k (6) = 32.2 - 28300/RT, beide 1. Ordnung) lassen auf konzertiert verlaufende [σ2s + σ2s + σ2s]-Cycloreversionen schließen. [3,6-12C2]-markiertes 4 liefert bei der Thermolyse ein trans-Bicyclo[4.3.0]nona-3,7-dien (31 ≙ 22) mit einem 12C-Markierungsmuster, das einen dreistufigen Bildungsmechanismus beweist. Dabei ist der erste Schritt wahrscheinlich eine [σ2s + σ2s + σ2s]-Cycloreversion mit ln k = 30.8 - 42000/RT (1. Ordnung). Nur das überbrückte 7 weicht diesem Umlagerungstyp aus und erfährt - offenbar aus Gründen der Ringspannung - eine schrittweise verlaufende [2 + 2]-Cycloreversion zu 18 und mindestens 5 Folgeprodukten.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 118 (1985), S. 2757-2776 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Bridgehead Olefinic Isomers of Triquinacene: Derivatives of Tricyclo[5.2.1.04,10]deca-1,5,8- and -1,6,8-trieneBridgehead halides 12 and 13 of triquinacene (2) with soft nucleophiles undergo a syn-stereoselective SN2′ reaction forming derivatives of tricyclo[5.2.1.04,10]deca-1,5,8-triene 15 and 17, respectively, and of tricyclo[5.2.1.04,10]deca-1,6,8-triene 18. The relative stability of these bridgehead olefins is discussed with regard to force field calculations as well as semiempirical MNDO calculations.
    Notes: Brückenkopf-Mono- 12 und -Dihalogenide 13 des Triquinacens (2) reagieren mit weichen Nucleophilen im Sinne einer syn-stereoselektiven SN2′-Reaktion zu Derivaten des Tricyclo[5.2.1.04,10]-deca-1,5,8-triens 15 bzw. 17 und des Tricyclo[5.2.1.04,10]deca-1,6,8-triens 18. Die relative Stabilität dieser Brückenkopf-Olefine wird anhand von Kraftfeld-Rechnungen sowie semiempirischen MNDO-Rechnungen diskutiert.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 116 (1983), S. 1377-1385 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Diademane and Structurally Related Compounds, II. Catalytic Rearrangements and HydrogenationsCopper, silver, gold, and rhodium compounds catalyze the rearrangement of diademane (1) to triquinacene (5) and snoutene (7), respectively. Known mechanisms may be adopted to explain this behaviour. The catalytic hydrogenation of 1 leads to a mixture of 6 products, 9-14, the composition of which was independent of the extent of reaction. Adamantane, the thermodynamically most stable isomer of all conceivable “hexahydrodiademanes”, was not detected.
    Notes: Kupfer-, Silber-, Gold- und Rhodiumverbindungen katalysieren die Umlagerung von Diademan (1) zu Triquinacen (5) bzw. Snouten (7). Zur Erklärung können bekannte Mechanismen herangezogen werden. Die katalytische Hydrierung von 1 führt zu den 6 Produkten 9-14 in einer vom Umsetzungsgrad unabhängigen Zusammensetzung. Adamantan, das thermodynamisch stabilste aller möglichen “Hexahydrodiademane”, konnte nicht nachgewiesen werden.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 118 (1985), S. 3993-4005 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Epoxidation of Barrelene: Preparation and Properties of OxahomobarrelenesA four-step synthesis makes barrelene (1) readily accessible on a 1 - 2 g scale. Upon epoxidation with KHCO3-buffered m-chloroperbenzoic acid 1 yields the mono- (2b), both the endo,exo- and exo,exo-isomeric bis- (3b and 4b) as well as the trisepoxide 5b. In the presence of traces of acid 2b very rapidly rearranges to cycloheptatriene-7-carbaldehyde (15), 5b undergoes a facile acid-catalyzed rearrangement to 4,7,11-trioxatrishomocubane (16). Under basic and neutral conditions 5b is stable towards virtually any nucleophile, its three epoxide rings can only be opened under reductive conditions with solvated electrons. On the other hand, endo,exo-dioxadihydrobishomobarrelene 20 and oxatrishomobarrelene 23 are readily attacked at the oxirane rings by lithium iodide/disodium hydrogen phosphate.
    Notes: In einer nur vierstufigen Synthese ist Barrelen (1) im Maßstab von 1 - 2 g rasch zugänglich. Bei der Epoxidation von 1 mit KHCO3-gepufferter m-Chlorperbenzoesäure werden das Mono- (2b), die endo,exo- und exo,exo-Isomeren Bis- (3b bzw. 4b) sowie das Trisepoxid 5b erhalten. In Gegenwart von Säurespuren lagert sich 2b sehr leicht in Cycloheptatrien-7-carbaldehyd (15), 5b leicht in 4,7,11-Trioxatrishomocuban (16) um. Unter basischen und neutralen Bedingungen ist 5b gegen alle möglichen Nucleophile stabil, lediglich durch Reduktion mit solvatisierten Elektronen lassen sich alle drei Epoxidringe öffnen. endo,exo- Dioxadihydrobishomobarrelen 20 und Oxatrishomobarrelen 23 werden dagegen von Lithiumiodid/Dinatriumhydrogenphosphat an den Oxiranringen glatt angegriffen.
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