Mechanistic Investigation of the Isomerization of 5-Vinyl-2-norbornene

Department of Chemistry, Kyung Hee University, Sŏul, Seoul, South Korea
The Journal of Organic Chemistry (Impact Factor: 4.72). 02/2006; 71(3):911-4. DOI: 10.1021/jo0518203
Source: PubMed


The isomerization reaction of 5-vinyl-2-norbornene (VNB) to 5-ethylidene-2-norbornene (ENB) has been performed using a catalytic system consisting of an alkali metal hydride and an amine. Among various amines tested, only aliphatic 1,2-diamines exhibited the activity for the isomerization. The isomerization was also affected by the alkali metal hydride employed. The activity of the alkali metal hydride increased with the increasing size of alkali metal: KH > NaH > LiH. A series of electron paramagnetic resonance (EPR) and UV-vis experiments on the active species suggest that the isomerization of VNB proceeds through a radical mechanism.

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    ABSTRACT: The preparation of potassium hydride as a 1:1 homogenate with paraffin, termed KH(P), is reported. KH(P), a solid at room temperature, is stable without special handling. On suspension in THF with a phosphonium salt, KH(P) rapidly generates the ylide. Wittig condensation with aromatic, aliphatic, and alpha,beta-unsaturated aldehydes proceeds with high Z selectivity. KH(P) should be a generally useful base for organic synthesis.
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    ABSTRACT: The last reviews devoted to the synthesis of 5-vinyl-2-norbornene and its isomerization to 5-ethylidene-2-norbornene were published in 1976–1977. The interest in the practical and theoretical aspects of this problem still does not wane, thus stimulating further investigations. A large number of patents and scientific articles have been published in the last 30 years and need to be summarized. This review elucidates the state of art of manufacture of 5-ethylidene-2-norbornene, the best third monomer for ethylene-propylene rubber. The results of new investigations concerning the manufacture of 5-vinyl-2-norbornene and its isomerization to 5-ethylidene-2-norbornene and vinylnortricyclene are considered. The most active base and coordination catalysts that have found application in industry are characterized. The mechanisms and stereochemistry of 5-vinyl-2-norbornene isomerization are discussed.
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    ABSTRACT: Various sodium-coated metal oxide catalysts were prepared using readily available supporting materials such as neutral γ-Al2O3 (neutral alumina, N-Al2O3) basic γ-Al2O3 (basic alumina, B-Al2O3), SiO2, MgO, and TiO2, and their catalytic activities were evaluated for the isomerization of 5-vinyl-2-norbornene (VNB) to 5-ethylidene-2-norbornene (ENB). Of various sodium-coated catalysts, Na/N-Al2O3 and Na/B-Al2O3 showed extremely high activities, resulting in quantitative conversion of VNB. Catalyst characterization and isomeri-zation results clearly demonstrated that the presence of both strong basic sites (pKBH ≥ 27) and one-electron donor sites on the Na/Al2O3 is prerequisite for the isomerization of VNB to take place.
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