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  • 1
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Two isomeric propellane epoxides 1a and 1b containing a cyclohexadiene ring are attacked by the title dienophile as predicted, syn to the five-membered ether ring whose α-hydrogens exert less repulsion than the α-epoxy hydrogens or the epoxide oxygen, respectively, of the cyclobutane ring.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 153-160 
    ISSN: 0947-3440
    Schlagwort(e): Valence isomerization ; Diazoketons ; Cycloadditions ; Steric hindrance ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Small Rings, 87. - Search for Alternative Routes to Tetra-tert-butyltetrahedrane; Synthesis of Sterically Overcrowded MoleculesKetene 3 can be isomerized to triclopentanone 2 by treatment with silica gel. Thus, the yield of tetrahedrane 5, which is formed upon irradiation of 2, has been improved. On the other hand, diazoketone 10 cannot be used as a precursor for 2. This failure is due to steric hindrance. For the same reason cyclobutadiene 4 is a very poor candidate for Diels-Alder cycloadditions.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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  • 3
    ISSN: 0947-3440
    Schlagwort(e): Matrix isolation ; Photochemistry ; CHNO isomers ; Hydrogen-bonded complexes ; Density functional calculations ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The complex photochemistry of matrix-isolated dihaloformoximes 8a, 8b, and 8c, which are transformed upon irradiation into the new hydrogen-bonded complexes HalCN…HOHal 10a-c′, identified by their IR spectra, has been unveiled. An earlier assignment of the experimental IR absorptions to isofulminic acid HONC (4) must be withdrawn. A competitive reaction to the formation of complexes 10a-c′ produces the hydrogen-bonded complexes HalNCO/HHal 12a-c′, which can be regarded as intermediates on the photochemical pathway to the final product isocyanic acid HNCO (1), and are tentatively identified by their IR absorptions. Our findings are supported by deuteration experiments and theoretical calculations using the density functional method BLYP/6-311G*.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 4
    ISSN: 0947-3440
    Schlagwort(e): Halogen addition ; Autoxidation ; Redox chemistry ; Oxetes, stable ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Small Rings, 88. - Reactions of Tetra-tert-butyltetrahedrane: Oxidation to the Radical Cation as the First StepThe chemistry of tetrahedrane 1 and cyclobutadiene 3 is governed by the initial formation of radical cation 2. In spite of the high steric hindrance 2 cannot be isolated as a radical-ion pair. Reaction of 3 with O2 generates the oxete 21 which is surprisingly stable (up to 200°C).
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 173-186 
    ISSN: 0947-3440
    Schlagwort(e): Tetrahedranes ; Cyclobutadienes ; Azetes ; Cyclopropenyldiazomethanes ; Pyridazines: chirality, ring inversion, valence isomers ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Small Rings, 90. - Peralkyl-Substituted TetrahedranesPhotolysis of the diazo compounds 4a, b generates adaman-tyltri-tert-butyltetrahedrane (9a) and tri-tert-butylisopropyltetrahedrane (9b), and the corresponding cyclobutadienes 10a, b. In contrast to tetrahedrane 9a, which results from an intramolecular addition in carbene 7a and also from photoisomerization of cyclobutadiene 10a, the only source for tetrahedrane 9b is the cheletropic cycloaddition of the carbenic center to the cyclopropene double bond in the photochemically produced carbene 7b. Tetrahedrane 9b is remarkable in its kinetic and thermal instability, which is caused by the reduced „corset effect“ in this compound. An additional access to this tetrahedrane is possible via the diazomethanes 34A and 34B. The pyridazines 17b and 41, which are formed by thermolysis of the diazo compounds 4b, 34A and 34B lead to the azetes 19 and 43. Last but not least 17b and 41 are interesting molecules themselves because of their inherent chirality.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 139-145 
    ISSN: 0947-3440
    Schlagwort(e): Nucleophilic addition ; Sigmatropic rearrangement ; Steric hindrance ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Small Rings, 85.  -  Attempts to Synthesize Alkyltri-tert-butyltetrahedranes by the Cyclopentadienone Route; Synthesis of the CyclopentadienonesStarting from 2-bromotri-tert-butylcyclopentadienone (1) a series of highly substituted cyclopentadienones has been prepared, hoping that they might be suitable candidates for the synthesis of a variety of tetrahedranes with different sterically demanding substituents.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 169-172 
    ISSN: 0947-3440
    Schlagwort(e): Cyclobutadiene ; Tetrahedrane ; Azete ; Cyclopropenyldiazomethane ; Valence isomers of pyridazine ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Small Rings, 89. - An Alternative Synthesis of Tetra-tert-butyltetrahedraneCyclopropenyldiazomethane 3 is an ideal precursor for tetra-tert-butyltetrahedrane (6). Both, photochemical and thermal decomposition of 3 lead to cyclobutadiene 7, which can be photoisomerized to tetrahedrane 6. Tetra-tert-butyltetrahedrane (6) is also formed directly by a cheletropic cycloaddition of the carbenic center to the cyclopropene double bond in carbene 4. This is the first example for the synthesis of a tetrahedrane, which does not occur via the corresponding cyclobutadiene. The formation of pyridazine 10 dominates the thermolysis of 3. Azete 12 is obtained both by photolysis as well as by thermolysis of Dewar-pyridazine 11, the irradiation product of 10.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 317-326 
    ISSN: 0947-3440
    Schlagwort(e): Matrix isolation ; IR spectroscopy ; Photochemistry ; Ab initio calculations ; Alkene complexes ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The matrix-isolated ethylene-bromine complex (1) and the cyclopropene-bromine complex (8) have been chosen to examine which ab initio method (MP2 or BLYP) is more suitable to calculate the IR spectra and structures of π complexes. In addition the photochemistry of 1 and 8 has been investigated and the mechanism of the photochemically induced reactions is discussed.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1980 (1980), S. 798-813 
    ISSN: 0170-2041
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Beschreibung / Inhaltsverzeichnis: Small Rings, 271).  -  Attempts to Synthesize AzacyclobutadienesHerrn Professor Matthias Seefelder zum 60. Geburtstag gewidmet.Photolysis of oxazinones 5 at low temperature yields the bicyclic valence isomers 8 and the ringopened ketenes 4 which can be characterized spectroscopically. Photoelimination of CO2 from bicyclus 8d gives azacyclobutadiene (azete) 2d, as indicated by the fragmentation pattern. The results of matrix irradiation of cyclopropenyl azides, 1,2,3- and 1,2,4-triazines also prove that azacyclobutadienes undergo ready cleavage into the corresponding nitriles and acetylenes.
    Notizen: Bei der Tieftemperaturphotolyse von Oxazinonen 5 können die bicyclischen Valenzisomeren 8 und die durch Ringöffnung entstehenden Ketene 4 spektroskopisch charakterisiert werden. Die Photoeliminierung von CO2 aus dem Bicyclus 8d verläuft über das anhand des Fragmentierungsmusters nachgewiesene Azacyclobutadien (Azet) 2d. Die Ergebnisse der Matrixbestrahlung von Cyclopropenylaziden, 1,2,3- und 1,2,4-Triazinen sprechen gleichermaßen dafür, daß Azacyclobutadiene sehr leicht einer photochemischen Sekundärspaltung in die entsprechenden Nitrile und Acetylene unterliegen.
    Zusätzliches Material: 8 Tab.
    Materialart: Digitale Medien
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