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  • Life and Medical Sciences  (96)
  • Cycloadditions  (22)
  • Biochemistry and Biotechnology
  • Physics
  • Wiley-Blackwell  (118)
  • 1995-1999  (118)
  • 1940-1944
  • 1999  (118)
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  • Wiley-Blackwell  (118)
Years
  • 1995-1999  (118)
  • 1940-1944
Year
  • 1
    Electronic Resource
    Electronic Resource
    3,5-Dimesityl-1,2,4-oxadiphosphole - Synthesis and Reactivity of a Novel Heterocycle (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 587-595 
    Details
    ISSN: 1434-193X
    Keywords: Phosphaalkenes ; Heterodiphospholes ; Cycloadditions ; Phosphaalkyne cyclooligomers ; Phosphorus-carbon cage compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The first synthesis of a 1,2,4-oxadiphosphole 6 has been achieved by vacuum thermolysis of mesitylphosphaalkene 5. The novel heterocycle 6 exhibits an enormous potential for cycloaddition reactions, which predominantly proceed selectively at low temperatures. Compound 6 undergoes addition with two equivalents of phosphaalkynes 10 by a [4+2] cycloaddition/homo Diels-Alder reaction sequence to form novel oxatetraphosphadeltacyclenes 12 and 13. Tetrachloro-o-benzoquinone (14) undergoes a selective [4+1] cycloaddition with 12 and 13 leading to the spirocyclic products 15 and 16 containing λ5-phosphorus atoms. Treatment of the oxadiphosphole 6 with dimethyl acetylenedicarboxylate (17) provides the first access to a 1,2-oxaphosphole 18, which is formed after an initial [4+2] cycloaddition followed by a retro Diels-Alder reaction. An unexpected reaction of 6 is observed with tri-tert-butylazete (20) furnishing a new polycyclic system (→ 21).
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  • 2
    Electronic Resource
    Electronic Resource
    On the Behavior of 5,8-Bis(trimethylsilyl)cycloocta-1,3,6-triene in Cycloaddition Reactions and Subsequent Chemistry (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1041-1050 
    Details
    ISSN: 1434-193X
    Keywords: Phosphaalkynes ; Cycloadditions ; Polycycles ; Cage compounds ; λ3-Phosphinines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Phosphaalkynes 2 and electron-deficient alkynes 11 readily react in a [4 + 2] cycloaddition process with 5,8-bis(trimethylsilyl)cycloocta-1,3,6-triene (8) in its bicyclic form 10 to furnish regioselectively the tricyclodecadienes 12 and 13, respectively. The phosphorus-containing compounds 12 exhibit structural features which make them suitable for homo-Diels-Alder reactions with electron-deficient acetylenes. A single crystal structure analysis of the homo-Diels-Alder adduct 14b confirmed the structure and relative configuration of the phophatricyclodecadienes 12. In solution the tricyclodecadienes 13 are prone to facile cycloreversion yielding the phthalic esters 15 and the cyclobutene 16. The latter is rapidly converted into the corresponding 1,3-butadiene 18, which can be trapped in a Diels-Alder/phospha-ene/Diels-Alder tandem reaction sequence by phosphaalkyne 2a. The phosphatricyclodecadiene 12 is thermally more stable; loss of cyclobutene 16 only occurs under FVP conditions to afford the λ3-phosphinine 22.
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  • 3
    Electronic Resource
    Electronic Resource
    Synthesis of Novel Steroid Alkaloids by Cyclization of Arylimines from Estrone (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3013-3020 
    Details
    ISSN: 1434-193X
    Keywords: Cycloadditions ; Domino reactions ; Iminium ions ; Lewis acids ; Quinolines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Intramolecular Lewis or Brønsted acid-catalyzed cyclization reactions of steroid arylimines 6 yielded either tetrahydroquinolines condensed to the estrane skeleton 9 or N-arylamino-D-homosteroids 12-16, depending on the substituent of the arylimino group.
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  • 4
    Electronic Resource
    Electronic Resource
    The Addition Patterns of C60 Trisadducts Involving the Positional Relationships e and trans-n (n = 2-4): Isolation, Properties, and Determination of the Absolute Configuration of Tris(malonates) and Tris[bis(oxazolines)] (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3027-3039 
    Details
    ISSN: 1434-193X
    Keywords: Chirality ; Circular dichroism ; Cycloadditions ; Fullerenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of regioisomeric trisadducts of C60 (5-11, 14-18) having the positional relationships e and trans-n (n = 2-4) resulting from successive additions of malonates or bis(oxazolines) to [6,6]-double bonds of the fullerene framework has been isolated and characterized. The new adducts 8-11 and 15-17 represent examples of unprecedented addition patterns. The addition patterns of the new trisadducts with C2, Cs or C1 symmetry have been assigned on the basis of the known positional relationships of the addends in their precursor bisadducts, and those of the C2- or Cs-symmetric representatives have been verified by analysis of their NMR spectra. The absolute configurations of the adducts with inherently chiral addition patterns could be determined either by comparison of the calculated and experimental CD spectra of the bis(oxazoline) adducts or with knowledge of the absolute configurations of the chiral bisadduct precursors containing bis(oxazoline) addends. The CD spectra of the pairs of diastereomers with an enantiomeric addition pattern fA -15/fC -15, fA -16/fC -16, and fA -18/fC -18 show mirror image behavior and pronounced Cotton effects.
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  • 5
    Electronic Resource
    Electronic Resource
    From 1,2,4-Triazines and Tributyl(ethynyl)tin to Stannylated Bi- and Terpyridines: The Cycloaddition Pathway (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 313-321 
    Details
    ISSN: 1434-193X
    Keywords: Cycloadditions ; Cross-coupling ; Halogens ; Nitrogen heterocycles ; Tin ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Recently, we reported on cycloadditions between electron-deficient heterodienes and tributyl(ethynyl)tin, which provide a new pathway to stannylated pyridazines and, in one special case, pyridines. In order to broaden the synthetic scope of these reactions, we have developed hetero [4+2] cycloaddition reactions between a number of tailor-made 1,2,4-triazines 5-9 (acting as heterodienes), and tributyl(ethynyl)tin (acting as dienophile). The desired 1,2,4-triazines are readily available, in moderate to very good yields, by the condensation reactions of appropiate carbamidrazones and glyoxals. These cycloadditions open up a novel route to regiospecifically stannylated 2,2′-bi- and 2,2′,6′,2′′-terpyridines 1-4, 11 in good yields. The stannanes 1-4, 11 are versatile synthetic intermediates, and with this strategy various substituents can be incorporated directly by substitution of the stannyl group, as was shown for halogens and carbon electrophiles under Stille conditions.
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  • 6
    Electronic Resource
    Electronic Resource
    An Efficient Synthetic Approach to Substituted Penta- and Hexahelicenes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3155-3163 
    Details
    ISSN: 1434-193X
    Keywords: Arenes ; Helical structures ; Cycloadditions ; NMR spectroscopy ; Semiempirical calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A two-step synthetic approach to penta- and hexahelicenes substituted at the terminal aromatic rings has been studied. This approach is based on the Diels-Alder reaction of 5,5′,8,8′-tetramethyl-3,3′,4,4′-tetrahydro-[1,1′]-binaphthalene (2b), 3-vinyl-1,2-dihydronaphthalene (5a), 5,8-dimethyl-3-vinyl-1,2-dihydronaphthalene (5b) and 3-vinyl-1,2-dihydrophenanthrene (15) followed by the aromatization of the cycloadducts. This method is flexible, efficient and of wide application to the synthesis of several benzenoid and nonbenzenoid penta- and hexahelicenes. The racemization energy barriers of helicenes 3, 9, 10, 13, 14, 17 and 18 were computed with the semiempirical quantum method AM1. The computed values show that, when methyl groups are introduced at the inner position of the terminal aromatic rings, the racemization barriers increase markedly. A structure analysis of the reaction products by 1H- and 13C-NMR spectroscopy is also presented.
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  • 7
    Electronic Resource
    Electronic Resource
    Synthesis, X-ray Crystal Structures and Reactivity Towards Alkynes of Gold(I)-Phosphinine Complexes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2233-2241 
    Details
    ISSN: 1434-1948
    Keywords: Phosphorus ; Heterocycles ; Phosphinines ; Gold ; Cycloadditions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The coordination behaviour of 2,6-disilyl-substituted phosphinines towards gold(I) has been examined. The reaction of the bis(trimethylsilyl)phosphinine 1 with [AuCl(SMe2)] gives the corresponding AuCl derivative 2. X-ray crystal structure analysis reveals that the aromaticity of the phosphinine ring is slightly reduced as a result of the poor π-back bonding ability of the AuCl fragment. The same phenomenon is observed in the cationic complex [Au(1)2][GaCl4] (3) which was readily prepared by reaction of two equivalents of 1 with [AuCl(SMe2)] followed by treatment with GaCl3 at low temperature. Reaction of 2,6-bis(phenylethynyldimethylsilyl)phosphinine (4) with the same precursor leads similarly to the complex [AuCl(4)] (5). Interestingly, this complex dimerizes upon crystallization to give the bis(phosphabarrelene) complex 6, also structurally characterized. The formation of 6 results from a [4 + 2] cycloaddition between one alkynyl group of each phosphinine with the other phosphinine subunit. The formation of the cationic complex [Au(4)][GaCl4] (8) occurs under classical conditions but it disproportionates to give the cationic complex [Au(4)2][GaCl4] (9) and colloidal gold deposition. The formation of 9 has been ascertained by treating 8 with one equivalent of ligand 4. Additionally, 9 can also be obtained in a straightforward fashion by treating two equivalents of 4 with [AuCl(SMe2)] followed by treatment with GaCl3 at low temperature. The structure of 9 has been elucidated. Despite a particular arrangement of the alkyne groups which encapsulate the gold coordination sphere, no gold-alkyne interactions are visible.
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  • 8
    Electronic Resource
    Electronic Resource
    Silylene Reactions with Buta-1,3-diynes: Cycloadditions, Insertions, and Rearrangements (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2301-2307 
    Details
    ISSN: 1434-1948
    Keywords: Multiple bonds ; Silicon ; Silylene ; Cycloadditions ; Insertions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Di-tert-butylsilylene, generated by photolysis of hexa-tert-butylcyclotrisilane 1 or 1,1-di-tert-butyl-trans-2,3-dimethyl-silirane (2), reacts with the 1,3-diyne (tBu-C≡C-)29 to furnish the dialkynylsilane 11 via the isolable alkynylsilirene 10. Photolysis of excess 1 in the presence of 9 furnishes the C-C linked 2,2′-disilirene 12 which, upon prolonged irradiation, rearranges to the 2,5-disilabicyclo[2.2.0]hexa-1(6),3-diene (13). Treatment of 9 with diarylsilylenes, formed by irradiation of hexamethyl-2,2-dimesityltrisilane (3) or hexamethyl-2,2-bis(2,4,6-triisopropylphenyl)trisilane (4), gives the corresponding alkynylsilirenes 14 and 15, respectively. Photolysis of 1 or 2 in the presence of (Me3Si-C≡C-)216 yields the dialkynylsilane 17 which, on further reaction with 2, yields the 2,5-disilabicyclo[2.2.0]hexa-1(6),3-diene (18). Irradiation of 3 in the presence of 16 affords the cis- and trans-isomeric 1,3-dimethylene-2,4-disila-cyclobutane derivatives cis-21 and trans-21, presumably via a 1-silaallene intermediate. The structures of 12, 15, 18, cis-21, and trans-21 have been determined by X-ray crystallography.
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  • 9
    Electronic Resource
    Electronic Resource
    Improved Synthesis, Structure, and Cycloaddition Reaction of [34](1,2,4,5)Cyclophane (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1223-1231 
    Details
    ISSN: 1434-193X
    Keywords: Cyclophanes ; Barrelenophanes ; Semibullvalenophanes ; Cycloadditions ; Cyanoacetylenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The modified synthetic route to [34](1,2,4,5)cyclophane (3) provides gram quantities of this compound in fewer steps than the conventional routes. The cycloaddition of 3 with dicyanoacetylene (12) gave barrelenophane 13, which was transformed into semibullvalenophane 15 on photoirradiation. This transformation (13 → 15) is in sharp contrast to the case of Boekelheide's [24]barrelenophane, where cyclooctatetraenophane is obtained. The X-ray structural analyses of 3, 13, and 15 demonstrates their unique structures.
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  • 10
    Electronic Resource
    Electronic Resource
    Addition Chemistry of Rod-Shaped 1,6-Dicyanohexatriyne: Regioselectivity Control by the Remote Cyano Function (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2491-2500 
    Details
    ISSN: 1434-193X
    Keywords: Addition reactions ; Cycloadditions ; Dicyanohexatriyne ; Enediyne ; Regioselectivity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The addition of different alcohols, amines, thioalcohols, ethers, cycloalkanes, tin hydride, alkenes or alkadienes to 1,6-dicyano-1,3,5-hexatriyne (1) leads, with a pronounced regioselectivity, to a series of substituted 1-ene-3,5-diynes. The addition of alcohols, amines and thiols proceeds preferentially in a syn mode leading to diastereomers with an E configuration. The reaction with free radicals, on the other hand, proceeds in an anti addition mode. The [4+2] and [2+2] cycloadditions performed with 1 yielded unsaturated six- and four-membered ring adducts, respectively. The cyclobutene derivatives resulting from [2+2] cycloadditions underwent spontanous electrocyclic ring-opening reactions with the formation of butadiene derivatives. Nucleophilic additions to form 1 lead exclusively to products where the donor atom is bound at C-1. All the reactions, except the formation of 19, showed an excellent regioselectivity with respect to the preferred addition to a terminal C≡C triple bond.
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