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  • 1
    Publication Date: 1996-02-01
    Print ISSN: 0040-4039
    Electronic ISSN: 1873-3581
    Topics: Chemistry and Pharmacology
    Published by Elsevier
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  • 2
    ISSN: 0947-3440
    Keywords: Furans ; Phospholes ; Pyrroles ; Thiophenes ; 1,5-Electrocyclization ; Ylides ; Sigmatropic [1,3] carbon shift ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carbonyl ylide-like intermediates are involved in the 1,5-electrocyclization of the bicyclo[3.2.0]heptenes 3a-c. The activation barriers analyzed by the time- and temperature-dependence of the exo ⇌ endo isomerization of specifically deuterated derivatives or of the racemization of optically active derivatives turned out to be higher by Δ ΔG≠ ≥ 11 kcal/mol than those determined for the corresponding bicyclo [3.1.0]hexenes 1a-c. This result can be considered as an evidence for the electrocyclic nature of these ring openings due to the diminished Walsh character of cyclobutane bonds compared to cyclopropane bonds. A stereochemical analysis of the fragmentation of 2-oxabicyclo[3.2.0]heptene 3a to furan and ethene leads to the conclusion that a sigmatropic [1.3] carbon shift proceeding with inversion of the migarting carbon followed by stereospecific retro-Diels-Alder reaction is the major pathway for this reaction similar to the rearrangement and fragmentation of the corresponding carbocycle 3e.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 112 (1979), S. 2286-2295 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Stereochemistry of the Norcaradiene-Norcaradiene Rearrangement, III. The Photochemical Rearrangement of Optically Active [Norcaradiene ⇌ Cycloheptatriene] DerivativesThe stereochemical course of the photochemical norcaradiene-norcaradiene rearrangement benzophenonesensitized is studied for the optically active systems methyl-2,7 dimethyl[norcaradiene ⇌ cycloheptatriene]-7-carboxylate (1) and 2,7-dimethyl[norcaradiene ≥ cycloheptatriene]-7-carbonitrile (2). In both systems the rearrangement is highly stereoselective( 1 ≥ 92%, and 2 76%) and proceeds with inversion at the migrating carbon C-7 similar to the corresponding thermal rearrangement. In nitrile 2 an additional racemization of the starting material due to an epimerization of C-7 competes with the rearrangement. Stereoselective diradical processes of triplett states are postulated to explain these results.
    Notes: Der stereochemische Verlauf der mit Benzophenon sensibilisierten, photochemischen Norcaradien-Norcaradien-Umlagerung wird am Beispiel der optisch aktiven Systeme 2,7-Dimethyl-[norcaradien ⇌ cycloheptatrien]-7-carbonsäure-methylester (1) und -7-carbonitril (2) untersucht. In beiden Systemen erfolgt die Umlagerung ähnlich wie die entsprechende thermische Umlagerung mit hoher Stereoselektivität (1 ≥ 92% und 2 ≥ 76%) unter Inversion am wandernden Kohlenstoff C-7. Im Nitril 2 wird außerdem eine mit der Umlagerung konkurrierende Racemisierung des Ausgangsmaterials beobachtet, die auf eine Epimerisierung an C-7 zurückgeführt wird. Zur Erklärung der Ergebnisse werden stereoselektive, diradikalische Prozesse aus Triplettzuständen postuliert.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 110 (1977), S. 107-123 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Stereochemistry of the Norcaradiene-Norcaradiene Rearrangement, I. The Synthesis of Optically Active [Norcaradiene ⇌ Cycloheptatriene] DerivativesAnion 14 derived from treatment of 1,3,5-cycloheptatriene-7-carbonitrile (13) with n-butyllithium or lithium diisopropyl reacts with methyl iodide, deuterium oxide, and carbon dioxide to give the corresponding 7,7-disubstituted derivatives 2, 13-D, and 16. By a sequence of reactions 2 was transformed into the optically pure [norcaradiene ⇌ cycloheptatriene] systems 4 and 10. The equilibrium concentrations of the [norcaradiene ⇌ cycloheptatriene] systems 2-12 were determined by 1H n.m.r. mesurements at low temperatures.
    Notes: Das aus 1,3,5-Cycloheptatrien-7-carbonitril (13) mit n-Butyllithium oder Lithium-diisopropylamid erzeugte Anion 14 reagiert mit Methyliodid, Deuteriumoxid und Kohlendioxid ausschließlich zu den entsprechenden 7,7-disubstituierten Derivaten 2, 13-D, und 16. Aus 2 lassen sich durch eine Folge von Reaktionen die optisch reinen [Norcaradien ⇌ Cycloheptatrien]-Systeme 4 und 10 synthetisieren. Mit Hilfe der Tieftemperatur-1H-NMR-Spektroskopie wurden die Gleichgewichtskonzentrationen der [Norcaradien ⇌ Cycloheptatrien]-Systeme 2-12 ermittelt.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 112 (1979), S. 1168-1188 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Stereochemistry of the Norcaradiene-Norcaradiene Rearrangement, II. The Thermal Rearrangement of Optically Active [Norcaradiene ⇌ Cycloheptatriene] DerivativesThe stereochemical course of the thermal norcaradiene-norcaradiene rearrangement discovered by Berson and Willcott is studied for the optically active systems methyl 2,7-dimethyl[norcaradiene ⇌ cycloheptatriene]-7-carboxalate (3) and 2,7-dimethyl[norcaradiene ⇌ cycloheptatriene]-7-carbonitrile (4). In both systems the rearrangement is highly stereoselective and proceeds with inversion at the migrating carbon C-7 contrary to the predictions of the Woodward-Hoffmann rules. This result is discussed considering diradical transition states.
    Notes: Der stereochemische Verlauf der von Berson und Willcott entdeckten thermischen Norcaradien-Norcaradien-Umlagerung wird am Beispiel der optisch aktiven Systeme 2,7-Dimethyl[norcaradien ⇌ cycloheptatrien]-7-carbonsäure-methylester (3) und -7-carbonitril (4) untersucht. In beiden Systemen erfolgt die Umlagerung mit hoher Stereoselektivität. Entgegen den Voraussagen der Woodward-Hoffmann-Regeln wird in jedem Fall Inversion am wandernden Kohlenstoff C-7 gefunden. Das Ergebnis wird unter dem Aspekt diradikalischer Übergangszustände diskutiert.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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