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  • Wiley  (91,257)
  • Wiley-Blackwell
  • 2000-2004  (91,752)
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  • 1
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    Climate change and Arctic ecosystems: 2. Modeling, paleodata‐model comparisons, and future projections (2003)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Atmospheres, Wiley, 8171 p., ISSN: 0148-0227
    Details
    Publication Date: 2019-08-23
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
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    Palaeoclimate reconstruction on Big Lyakhovsky Island, north Siberia—hydrogen and oxygen isotopes in ice wedges (2002)
    Wiley
    In:  EPIC3Permafrost and Periglacial Processes, Wiley, 13(2), pp. 91-105, ISSN: 1045-6740
    Details
    Publication Date: 2023-07-06
    Description: Late Quaternary permafrost deposits on Big Lyakhovsky Island (New Siberian Islands, Russian Arctic) were studied with the aim of reconstructing the palaeoclimatic and palaeoenvironmental conditions of northern Siberia. Hydrogen and oxygen stable isotope analyses are presented for six different generations of ice wedges as well as for recent ice wedges and precipitation. An age of about 200 ka BP was determined for an autochtonous peat layer in ice-rich deposits by U/Th method, containing the oldest ice wedges ever analysed for hydrogen and oxygen isotopes. The palaeoclimatic reconstruction revealed a period of severe winter temperatures at that time. After a gap in the sedimentation history of several tens of thousands of years, ice-wedge growth was re-initiated around 50 ka BP by a short period of extremely cold winters and rapid sedimentation leading to ice-wedge burial and characteristic ice-soil wedges (‘polosatics’). This corresponds to the initial stage for the Late Weichselian Ice Complex, a peculiar cryolithogenic periglacial formation typical of the lowlands of northern Siberia. The Ice Complex ice wedges reflect cold winters and similar climatic conditions as around 200 ka BP. With a sharp rise in υ18O of 6‰ and υD of 40‰, the warming trend between Pleistocene and Holocene ice wedges is documented. Stable isotope data of recent ice wedges show that Big Lyakhovsky Island has never been as warm in winter as today.
    Repository Name: EPIC Alfred Wegener Institut
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  • 3
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    Late Saalian and Eemian palaeoenvironmental history of the Bol'shoy Lyakhovsky Island (Laptev Sea region, Arctic Siberia) (2004)
    Wiley
    In:  EPIC3Boreas, Wiley, 33(4), pp. 319-348, ISSN: 0300-9483
    Details
    Publication Date: 2024-04-25
    Description: Palaeoenvironmental records from permafrost sequences complemented by infrared stimulated luminescence (IRSL) and 230Th/U dates from Bol'shoy Lyakhovsky Island (73°20′N, 141°30′E) document the environmental history in the region for at least the past 200 ka. Pollen spectra and insect fauna indicate that relatively wet grasssedge tundra habitats dominated during an interstadial c. 200-170 ka BP. Summers were rather warm and wet, while stable isotopes reflect severe winter conditions. The pollen spectra reflect sparser grass-sedge vegetation during a Taz (Late Saalian) stage, c. 170-130 ka BP, with environmental conditions much more severe compared with the previous interstadial. Open Poaceae and Artemisia plant associations dominated vegetation at the beginning of the Kazantsevo (Eemian) c. 130 ka BP. Some shrubs (Alnus fruticosa, Salix, Betula nana) grew in more protected and wetter places as well. The climate was relatively warm during this time, resulting in the melting of Saalian ice wedges. Later, during the interglacial optimum, shrub tundra with Alnus fruticosa and Betula nana s.l. dominated vegetation. Climate was relatively wet and warm. Quantitative pollen-based climate reconstruction suggests that mean July temperatures were 4-5°C higher than the present during the optimum of the Eemian, while late Eemian records indicate significant climate deterioration. © 2004 Taylor & Francis.
    Repository Name: EPIC Alfred Wegener Institut
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  • 4
    Electronic Resource
    Electronic Resource
    Triphenylpyrylium Tetrafluoroborate-Sensitized Photochemistry of the Terpenes Sabinene, α-Phellandrene, and α- and γ-Terpinene (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1563-1567 
    Details
    ISSN: 1434-193X
    Keywords: Triplet recombination ; Electron transfer ; Radical ions ; Photochemistry ; Terpenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The triphenypyrylium tetrafluoroborate (TPT)-sensitized reactions of several terpene donor molecules, including sabinene (1), α-phellandrene (4), α-terpinene (5) and γ-terpinene (6) give rise to significantly different products than reactions induced by other electron-transfer sensitizers, such as 1,4-dicyanobenzene (DCB). The divergent reactions require decidedly different key intermediates; the products obtained with TPT can be explained by dissociative recombination of the intermediate radical-radical cation pair in the triplet state, generating donor-derived biradicals.
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  • 5
    Electronic Resource
    Electronic Resource
    Ring Expansion of 2-Alkylidenedihydroquinazolines to Iminodihydro-1,4-benzodiazepines by Methanesulfonyl and Trifluoromethanesulfonyl Azide (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1577-1587 
    Details
    ISSN: 1434-193X
    Keywords: Azides ; Cleavage reactions ; Cycloadditions ; Nitrogen heterocycles ; Polycycles ; Ring expansion ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---2-Alkyl-1-methylquinazolinium hexafluorophosphates 9 are deprotonated by sodium or potassium hydride to afford solutions of 2-alkylidenedihydroquinazolines 10, which were investigated by NMR spectroscopy. Trapping with methanesulfonyl azide (5a) of 10 in situ or subsequent treatment with trifluoromethanesulfonyl azide (5b) gives mixtures of colourless (15) and intensely yellow N-sulfonylimino-1,4-benzodiazepines 16 along with products due to cleavage of the exocyclic double bond of 10, viz. 11 and 13. The ethylidene compound 10b yields the bicyclic products 18 and 19, apparently by complex sequences of reactions that are triggered by removal of the acidic proton at C-2 of 16b and 16f. The structures of the products are based on spectroscopic evidence and X-ray diffraction analyses performed on 15b, 16d, 16e, and 19.
    Additional Material: 6 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Electrophilic Reactivity of a 2-Azaallenium and of a 2-Azaallylium Ion (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1589-1593 
    Details
    ISSN: 1434-193X
    Keywords: Azaallenium ions ; Azaallylium ions ; Iminium ion ; Kinetics ; Linear Free Energy Relationships ; Ab initio calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The rate constants for the reactions of the 2-azaallenium ion 1b+, the 2-azaallylium ion 2a+ and the iminium ion 3+ with different nucleophiles were determined by 1H NMR spectroscopy. By correlation with the Linear Free Enthalpy Relationship (LFER) lg k20°C = s (E + N), developed by Mayr and Patz, the electrophilicity parameters E(1b+) = -3.7, E(2a+) ≍ -16 and E(3+) = -10.43 were obtained. They show that the relative reactivities of these ions are approximately 1012:1:106. Quantum chemical calculations (ab initio, DFT) of the methyl anion affinities for the ions 1b+,2a+ and3+ are in agreement with the experimental E values. The X-ray structure of 3+·CF3SO3- is reported for the first time; it shows no strong interaction between the cation and the anion.
    Additional Material: 2 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxazoline N-Oxide Mediated [3+2] Cycloadditions: Application to a Formal Synthesis of a (+)-β-Methylcarbapenem (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1595-1601 
    Details
    ISSN: 1434-193X
    Keywords: Oxazoline N-oxide ; Cycloadditions ; Cycloadditions ; Lactams ; Thienamycin ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---[3+2] Cycloaddition between a camphor-derived oxazoline N-oxide 9 and the γ,δ-unsaturated enamino ester 11 afforded the single adduct 6. A stereoselective reduction of the enamino ester side chain allowed the control of the absolute configuration of the two additional asymmetric centres. Nitrogen protection and oxidative hydrolysis of the resulting product 13, followed by further functional group manipulations, led to the β-lactam derivative 1, a known precursor of the β-methylthienamycin derivative2a.
    Additional Material: 1 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    A New Substitution Pattern in Subphthalocyanines: Regioselective Synthesis and Separation of “ortho” Derivatives (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1603-1607 
    Details
    ISSN: 1434-193X
    Keywords: Boron ; Cyclotrimerizations ; Nitrogen heterocycles ; Macrocycles ; Subphthalocyanines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The regioselective preparation of ortho-substituted subphthalocyanides was achieved employing 3-substituted phthalonitrile derivatives as starting materials. A mechanistic proposal has been outlined.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/99525_s.pdf or from the author.
    Additional Material: 2 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    A New Route to 2,7- and 7-Functionalized Labdanes (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1609-1615 
    Details
    ISSN: 1434-193X
    Keywords: Terpenoids ; Natural products ; Total synthesis ; Cyclizations ; Rearrangements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A new route for the synthesis of 2,7- and 7-functionalized labdanes starts from (R)-carvone (1). 11-Nordrim-7-en-9-one (15) is an appropriate starting material for the total synthesis of hispanone (21), a biologically active furolabdane isolated from the Mediterranean medicinal plant Ballota saxatilis.
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  • 10
    Electronic Resource
    Electronic Resource
    Preparation of Kingiside from Aucubin (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1623-1626 
    Details
    ISSN: 1434-193X
    Keywords: Iridoid glucoside ; (8S)-Kingiside ; (8S)-Loganin ; (8S)-7-Ketologanin ; Asymmetric synthesis ; Natural products ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The tetraacetyl derivative 8 of the naturally occurring kingiside (8a) was prepared from aucubin (1). Intermediates in the synthesis were (8S)-tetraacetyl loganin (6) and (8S)-tetraacetyl-7-ketologanin (7), whose free (8R)-epimers occur in many different plants (Caprifoliaceae, Loganiaceae). The 13C NMR spectrum allows the structure to be unequivocally identified.
    Additional Material: 1 Tab.
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