ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Chemistry  (3)
  • 1980-1984  (1)
  • 1975-1979  (1)
  • 1915-1919  (1)
Collection
Publisher
Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 8 Tab.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Photochemistry of Tetraalkyl Substituted γ-Keto-olefinesThe photochemistry of 7,8-dihydro-β-ionone (1) in solution is shown to depend on temperature, polarity and viscosity of the solvent. UV. irradiation (λ ≥ 245 nm) in pentane at +25° converts 1 to the isomeric ethers 3 (16%), 5A (48%) and 5B (22%), whereas at -65° 7,8-dihydro-γ-ionone (26) is obtained in 12% yield together with 13% of 3, 12% of 5A and 9% of 5B. The 1n,π*-excitation of 1 in acetonitrile gives similar results. In the more viscous 1,2,3-triacetoxypropane the photoisomerization 1 → 26 takes place even at + 60° (10% yield, cf. 40% at -15°). In alcoholic solvents, however, no formation of 26 is detected, but the hitherto unknown [2+2]-photocycloaddition 1 → 11 can be observed (4% at -7°, 15% at -65S° in 2-propanol). An intermediate e may be involved (Scheme 14). In addition to the photoreactions 1 → 3, 5A, 5B and 11 the isomerization of 1 to the novel spirocyclic ketone 28 takes place in alcoholic solvents only.Photoisomerization 1 → 3 is presumably a photo-ene process involving a stereoselective intramolecular H-transfer. This type of photoisomerization is restricted to cyclic γ-keto-olefines. The tetraalkylated acyclic γ-keto-olefines 14 and 15 photoisomerize exclusively by [2+2]-cycloaddition, independent of the solvent.On 1n,π*-excitation the δ,∊-unsaturated bicyclic ketone 44 undergoes Norrish-Type-II photofragmentation to the diene 45 or isomerizes to the γ, ∊-unsaturated ketone 17. Competition between these two reactions is strongly temperature dependent: photolysis in pentane at -72° yields quantitatively 45, whereas at + 35° only 30% of 45 and 68% of 17 are obtained.UV. irradiation of the novel spirocyclic ketone 28 gives as primary photoproduct the isomeric aldehyde 29, and in a secondary photoreaction the isomeric oxetanes 30A and 30B. Experiments with deuteriated substrates show that the isomerization of type 28 → 29 is stereocontrolled.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Compounds of the 3,4-dihydro-ionone series as models for the photochemistry of γ, δ- and δ,∊- unsaturated ketones and aldehydes.The photochemistry of γ, δ- and δ,∊-unsaturated carbonyl compounds of the dihydro-ionone series has been studied, with special attention to the investigation of oxetane formation versus hydrogen abstraction.UV.-irradiation of the dihydro-β-ionone compounds with structure A (1, 7, 14, 18, 24, 29) led to isomeric ethers with structures B (2, 8, 15, 19, 25, 30), C (3, 9, 16, 20, 26, 31) and D (4, 21, 27), isomeric bicyclic alcohols with structure E (5, 10, 17, 22, 28), and photoreduction products with structure F (6, 11, 12, 13). Photolysis of dihydro-γ-ionone (32) gave a complex mixture containing fragmentation product 35, hydrocarbon 36, β-ambrinol (34), oxetane 33, as well as dihydro-β-ionone (1) and three of its photoproducts (2, 3, 5). The dihydro-α-ionone compounds 37 and 40 gave mixtures of fragmentation products and the oxetanes 38 and 41. Irradiation of the side-chain homologues 42 and 45 yielded 43, which photo-cyclizes to 44. In contrast, 3, 4-dihydro-3′,4′-dehydro-β-ionone (46) gave merely the isomeric open-chain triene-ketone 47.The structures assigned to the ethers 2, 3, 33, 38 and to the alcohols 5, 10, 13 could be confirmed by chemical reactions and mutual interconversions. The structure of the ether 21 had to be established by X-ray analysis, details of which are described.A novel intramolecular hydrogen transfer is involved in formation of ethers B. The photocyclization A → D probably proceeds by addition of the carbonyl-C atom to the double bond (A → h), followed by methyl (1 → 2)-shift (h → i). Process A → h may also be involved in formation of compounds of type C and E.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...