5-Vinyl-2-norbornene isomerization

The isomerization of 5-vinyl-2-norbornene to 5-ethylidene-2-norbornene has been performed using a catalytic system consisting of an alkali metal hydride and an amine. The activity of the alkali metal hydride increased with increasing size of the alkali metal KH > NaH > LiH. Among the various amines tested, only aliphatic 1,2-diamines exhibited the activity for the isomerization. Electron paramagnetic resonance (EPR) and UV-visible spectroscopic experiments on the active species suggest that the isomerization of 5-vinyl-2-norbornene proceeds through a radical mechanism.167... 

The lower molecular weight trimers (m/z=310) were separated and isolated using HPLC techniques. Based on their mass and the structures of the dimers, isomeric forms of vinyl-terminated trimers of norbornene were proposed for these two trimers. This was confirmed by extensive NMR analysis. The H and C... 

Asymmetric hydrovinylation of norbornene and norbornadiene leading exclusively to exo-vinyl products 4 and 5 has been reported with allylnickel systems using isopropylbis(men-thyljphosphane as chiral ligand4,5. Optical yields depend highly on temperature, highest enantiomeric excesses (up to 80.6%) are obtained at about — 70 =C. however with only low productivity. Furthermore, the products tend to isomerize to exo-methylene compounds under the reaction conditions. 

Diels-Alder reaction of cyclopentadiene and butadiene affords a mixture of exo-5-vinyl-2-norbornene (la) and e do-5-vinyl-2-norbornene (lb) [1], Preparative GC separation [1] of these isomers encounters difficulties in obtaining the individual isomer in pure form and in large quantities. An alternative approach of separation via thermal isomerization [2], in which lb gets transferred to 4,7,3a,7a-tetrahydro-lff-indene, whereas la remains unchanged, is also not successful. This is because it is difficult to prevent la being contaminated by unreacted lb. As no other method is available for their separation, Inoue has reported [3] that hydroboration of 1 with 9-BBN, followed by oxidation with alkaline hydrogen peroxide results in the formation of alcohols 2a and 2b. The iodoether cyclization only of the endo isomer takes place. The sequence of approach is delineated in Scheme 29.1. 

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