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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 120 (1987), S. 387-393 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: While the photolysis of crystalline trans,trans-2,5-dibenzylidenecyclopentanone (1, Ar=C6H5) yields three dimers in a latticecontrolled manner, the crystals of its symmetric derivatives 1 are photostable. The 2-alkylidene-5-arylidenecyclopentanones 4 and 5 yield selectively 6 or 8 (centrosymmetric) and oligomers. 4b gives 6 and 7. The 4-nitrophenyl and 4-pyridinyl substituents prove to be particularly effective in terms of the socalled crystal engineering due to their electrostatic effects. The occurance of oligomers shows that the unsymmetric derivatives 4 and 5 do not always react in a single topochemical way.
    Notes: Während die Kristallphotolyse von trans-2,5-Dibenzyliden-cyclopentanon (1, Ar=C6H5) gitterkontrolliert drei Dimere liefert, sind dessen kristalline symmetrische Derivate 1 photostabil. Die 2-Alkyliden-5-arylidencyclopentanone 4, 5 liefern neben Oligomeren selektiv 6 oder 8 (zentrosymmetrisch). Aus 4b entsteht neben 6 auch 7. 4-Nitrophenyl- und 4-Pyridinylgruppen erweisen sich wegen ihrer elektrostatischen Effekte als besonders wirksam im Hinblick auf die gezielte Kristallgestaltung. Die Oligomerenbildung zeigt, daß nicht alle unsymmetrischen Derivate 4, 5 topochemisch einheitlich reagieren.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Reactions with Phosphinealkylenes, XXXIX.  -  New Methods for the Preparation of 1-Bromoacetylenes and EnynesProf. Dr. M. Seefelder zum 60. Geburtstag.1,1-Dibromoolefins 4 are obtained in good yield from the reaction of aldehydes 1 with triphenyl-phosphane (2) and carbon tetrabromide (3). Reaction of 4 with three moles of methylene(triphenyl)phosphorane (8) leads to the propargylidene(triphenyl)phosphoranes 11 which react with aldehydes to give the enynes 13. The ylides 11 can also be prepared via the reaction of bromo-acetylenes 7, which can be obtained from 4, with two moles of 8. This reaction sequence allows the synthesis of new retinoids with enyne structures from retinal.
    Notes: Aus Aldehyden 1, Triphenylphosphan 2 und Tetrabrommethan 3 erhält man in guten Ausbeuten 1,1-Dibromolefine 4. Ihre Reaktion mit 3 Mol Methylen(triphenyl)phosphoran 8 führt zu den Propargyliden(triphenyl)phosphoranen 11, die sich mit Aldehyden zu den Eninen 13 umsetzen. 13 ist auch durch Reaktion der aus 4 erhältlichen Bromacetylene 7 mit 2 Mol 8 zugänglich. Die Reaktionsfolge ermöglicht den Aufbau neuer Retinoide mit Eninstruktur ausgehend von Retinal.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 121 (1988), S. 2127-2134 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: 1,2,3-Trimethylenecyclopentanes: Synthesis and ReactionsThe first 1,2,3-trimethylenecyclopentanes 3 are synthesized from bismethylenecyclopentanones 1 by a Wittig reaction in the presence of sodium bis(trimethylsilyl)amide. Several side and succeeding reactions occur. These yield cyclopropane derivatives 4, products of repeated reactions with phosphorus ylides (10 or the polyspirocyclopropanes 12 and 14), Diels-Alder dimers 5 and Diels-Alder adducts 7. All products are characterized spectroscopically. The title compounds 3 can be isolated only if suitable substituents impede the succeeding and competing reaction modes. The high reactivities of the system 3 (e.g. 3o→5o) are compared with those of the ring homologs (dimer 15, monomers 16, 17).
    Notes: Die ersten 1,2,3-Trimethylencyclopentane 3 werden aus Bismethylencyclopentanonen 1 durch Wittig-Reaktion in Gegenwart von Natrium-bis(trimethysilyl)amid synthetisiert und spektroskopisch charakterisiert. Neben- und Folgereaktionen führen zu Cyclopropan-Derivaten 4, Produkten mehrfachen Phosphorylid-Angriffs (10 sowie die Polyspirocyclopropane 12 und 14) und Diels-Alder-Dimeren 5 sowie -Abfangprodukten 7. Die Titelverbindungen 3 sind nur isolierbar, wenn geeignete Substituenten die Folge- und Nebenreaktionen erschweren. Die hohen Reaktivitäten des Systems 3 (z. B. 3o→5o) werden verglichen mit denen der Ringhomologen (Dimeres 15, Monomere 16, 17).
    Additional Material: 1 Tab.
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 121 (1988), S. 2135-2145 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Photoreactions in Crystals with Ethenes: Selectivities and Crystal EngineeringPhotoreactions in crystals of sterically hindered dimethylenecyclopentanones 1 and trimethylenecyclopentanes 4 lead to E/Z isomerizations and 1,5-H shifts. The stereochemical result of the photodimerization in the crystalline state of the heterostilbenes 6 is apparently determined by the polarity (dipole moment), which governs the crystal packing as well. A strong dissymmetry of charge (as in 6a-g) gives rise to H(ead)/T(ail)-syn dimers 7. This correlates well with the molecular stacking in the crystals of 6c, as determined by X-ray analysis. A low dissymmetry of charge (as in 6h) leaves the crystals photostable. At medium polarity two products with H/T-syn and H/H-syn stereochemistry (7 and 8) or, in particular cases, only dimers of type 8 are formed. The precise stereochemistry is proved by comparison with the analyzed 1H-NMR parameters of esters of truxillic and truxinic acids. Bifunctional heterostilbenes like 12c are photostable in the crystalline state. However, strongly polar methoxycarbonyl (13) and acetyl groups (17, 21) lead to photoreactive crystals again. In the case of 17 this is also shown by X-ray analysis. Due to well-defined possibilities of movement, there are three products formed in terms of multiproduct topochemistry, 13 and 21 also form several products upon photoreaction in the crystal.
    Notes: Die Photodimerisierung im Kristall von sterisch gehinderten Dimethylencyclopentanonen 1 und Trimethylencyclopentanen 4 führen zu E/Z-Isomerisierungen und 1,5-H-Verschiebungen. Bei den Heterostilbenen 6 bestimmt die Polarität (Dipolmoment) offenbar die Kristallpackung und das stereochemische Ergebnis der Kristallphotodimerisierung. Starke Ladungsasymmetrie (6a-g) führt zu K(opf)/S(chwanz)-syn-Dimeren 7 entsprechend der für 6c röntgenographisch ermittelten Molekülpackung im Kristall. Bei geringer Ladungsasymmetrie (6h) sind die Kristalle photostabil und bei mittlerer Polarität gibt es im Sinne der Mehrprodukte-Topochemie K/S-syn- und K/K-syn-Dimere (7 und 8), in Einzelfällen auch nur 8. Die Stereochemie wird durch Vergleich mit den 1H-NMR-Parametern von Truxill- und Truxinsäureestern belegt. Bifunktionelle Heterostilbene wie 12c sind im Kristall photostabil. Erst stark polare Methoxycarbonyl- (13) und Acetyl-Gruppen (17, 21) führen wieder zu photoreaktiven Kristallpackungen. Dies wird bei 17 auch durch Röntgenstrukturanalyse gezeigt. Wegen wohldefinierter Bewegungsmöglichkeiten entstehen drei Produkte. Auch 13 und 21 bilden mehrere Produkte bei der Photoreaktion im Kristall.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0570-0833
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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