Monosubstituted norbornenes

Here we shall adopt a uniform numbering system for norbomene derivatives, with the double bond always in the 2-position, even when it should strictly be numbered as the 5-position. This will make it easier to list and compare such compounds. 

Hydrogenation of polymers of substituted norbomenes is frequently a valuable aid to the determination of structural detail and is best carried out using diimide (NH—NH) generated in situ by the decomposition of p-toluenesulfonohydrazide in xylene at 120°C. This procedure works well and selectively even in the presence of groups such as COOMe and PPha (Sohn 1995). 

1 Norbomenes with an alkyl, alkenyl, or aryl substituent 

Couturier 1992). With 27 and 28 most catalysts give polymers with randomly oriented substituents (Ivin 1980b, 1981a). Thus the further away the substituent is from the double bond, the less effect it has on the head or tail orientation of the incoming monomer. In polymers of single enantiomers the orientation of the substituents in the polymer is correlated with the ring tacticity. Details are given in Ch. 11. 

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Norbornene derivatives bearing two alkynes undergo cascade enyne metathesis reactions when treated with a first generation ruthenium carbene and ethylene, giving heterocyclic dienes [28]. The ROM of the norbornene moiety initiates the cascade enyne RCM reactions (Scheme 14). When ethylene is replaced by a monosubstituted alkene, a single enyne RCM takes place, after the initial ROM of norbornene. 

Oxymercaration (2, 265-267 3. 194). Brown and Geoghegan have investigated the relative reactivities of a number of olefins in the oxymercuration reaction in a 20 80 (v/v) mixture of water and THF. The following reactivity is observed terminal disubstituted > terminal monosubstituted > internal disubstituted > internal trisub-stituted > internal leirasubstitu ted. Thus steric factors play a major role in the reactivity of olefins. Increased substitution on the double bond and increased steric hindrance at the site of hydroxyl or mercury substituent attachment decrease the rate of reaction. In the case of olefins of the type RCH CHR, cts-oleiins are more reactive than the corre.sponding rra/i.s-olefins. Inclusion of the double bond in ring systems causes a moderate rate increase which varies somewhat with structure cyclohcxenc > cyclo-pentenc cyclooctene norbornene bicyclo[2.2.2]-octene-2. 

The photocycloaddition of 2tf-azirines to electron-deficient olefins produces d -pyrrolines as primary photoproducts. Some of the dipolarophiles used include acrylic esters, acrylonitriles, fumaric and maleic esters, methyl allenecarboxylate, norbornene, and l,2-dicyanocyclobutene. Similarly, styrenes and vinylpyridines undergo smooth photocycloaddition to 2H-azirines. Addition of acetylene derivatives to the transient nitrile ylide gives 2H-pyrroles (18, 20) which rearrange to pyrroles (19) if the C-2 atom is monosubstituted. 3-Phenyl-2/f-azirines have been found to cycloadd to vinylphosphonium salts and to vinyl sulfones. The initial adducts (22 and 24) undergo ready loss of the phosphorous or sulfur substituent to give 2H-pyrroles (23 and 25). ... 

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