Norbornadienes, and

The reaction of o-iodophenol, norbornadiene and CO proceeds via alkene and CO insertions to afford the lactone 562, which is converted into coumarin (563) by the retro-Diels-Alder reaction. In this coumarin synthesis, norbona-diene behaves as a masked acetylene[4)3],... 

HC(17)1, p. 53), and by retro-Diels-Alder reaction of the adduct from norbornadiene and fulminic acid <67AG(E)456). 

P. B. Venuto and P. S. Landis On Transition Metal-Catalyzed Reactions of Norbornadiene and the Concept of a Complex Multicenter Processes G. N. SCHRAUZER... 

The cycloaddition between norbornadiene (23 in Scheme 1.12) and maleic anhydride was the first example of a /mmo-Diels-Alder reaction [55]. Other venerable examples are reported in Scheme 1.12 [56]. Under thermal conditions, the reaction is generally poorly diastereoselective and occurs in low yield, and therefore several research groups have studied the utility of transition metal catalysts [57]. Tautens and coworkers [57c] investigated the cycloaddition of norbornadiene and some of its monosubstituted derivatives with electron-deficient dienophiles in the presence of nickel-cyclo-octadiene Ni(COD)2 and PPhs. Some results are illustrated in Tables 1.4 and 1.5. 

The oxidation of norbornadiene and some derivatives using Pseudomonas sp [96]. 

There are several known examples of silenes participating in [2 + 2 + 2] cycloadditions, including reactions with norbornadiene and with quadricyclane. Examples of these reactions with norbornadiene are shown in Eq. (30), where the silene bridges the 2,6-positions.38 5, 53 ,7U85 ,88 This reaction has only been investigated using some of the Auner-type silenes. In many cases mixtures of stereoisomers were obtained, and in some cases products of an ene reaction were also observed. 

Kaupp and Prinzbach have shown that the sum of the quantum yields for the forward and reverse transformations of a number of norbornadienes and quadricyclanes is about unity(115 117) ... 

When irradiated in the presence of norbornadiene and high-pressure synthesis gas, rhodium chloride is converted to a catalyst which is active for a variety of reactions. /2A/. The salt is probably converted photochemically to the rhodium norbornadiene complex 9. This dimer may undergo a consecutive photoreaction to give the monomeric hydrido complex 10, which is the actual catalyst for polymerisation, hydrogenation, and hydroformylation reactions. 

Lautens and Snyder have shown that cobalt is an effective catalyst for the [4 + 2 + 2]-reaction of norbornadienes and 1,3-butadienes. Significant developments in this area include an enantioselective process described by Lautens146 and a catalyst system that gives increased yields as described by Snyder (Scheme 60).147,148... 

Y. Harel, A. W. Adamson, C. Kutal, P. A. Grutsch, K. Yasufuku. Photocalorimetry. 6. Enthalpies of Isomerization of Norbornadiene and of Substituted Norbomadienes to Corresponding Quadricyclenes. J. Phys. Chem. 1987, 91, 901-904. 

IV. CYCLIZATION OF NORBORNADIENES AND RELATED COMPOUNDS A. All Carbon Systems... 

The most efficient catalysts for the homo Diels-Alder reactions of norbornadiene were found to be cobalt327 and nickel328 complexes. The general mechanistic pathway that has been proposed for these reactions has been depicted in equation 161329. According to this mechanism, co-ordination of norbornadiene and the olefin or acetylene to the metal center gives 557, which is in equilibrium with metallocyclopentane complex 558. Then, insertion of the olefin or acetylene in the metal-carbon bond takes place to form 559. Reductive elimination finally liberates the deltacyclane species. 

Figure 4.3 Representative Cl mass Figure 4.4 Low-energy collision-spectra of quadricyclane showing changes indnced dissociation patterns for CyHs with flow tube temperature (a) 973 K isomers, showing clear differences (6) 573 K and (c) 298 K (a) quadricyclane (6) norbornadiene and...

Both quadricyclane and norbornadiene are high-energy isomers of C7H8, and it is interesting to compare their thermal behavior. Figures 4.5 and 4.6 show the pyrolysis breakdown behavior for norbornadiene and quadricyclane, respectively, extracted as described above. As shown, norbornadiene (NBD) is stable on the available time scale for temperatures up to 600 K. (The small apparent decrease in NBD contribution in the 400-600 K range is within the uncertainty of the fitting process — no product species are observed.) Above 600 K decomposition... 

Triazole and 8-azapurine derivatives 843 were prepared by the cyclocondensation of the acyclic azide derivative 842 with cyanoacetamide, norbornadiene, and acetylene derivatives (90H1669). 

Scheme 61) [2b, 150], but can give rise to a variety of products. With unsym-metrically substituted alkenes of type 266, two regioisomeric products were obtained, but the isomer 268 bearing the ester group near the spiro atom was the minor component in all cases. Norbornadiene and norbornene react with 1 by the same mode to give formal [3 -F 2] cycloadducts 269 and 270, respectively, the latter as a 9 1 mixture of exo- and endo-isomers. 

The rhodium complexes were prepared in situ from the rhodium precursor [Rh(nbd)2](C104) (nbd = 2,5-norbornadiene) and applied in the hydrogenation experiments under an initial hydrogen pressure of 5 bar at 35°C. The dendrimer structure had almost no effect on the activity of the catalyst in the batch-wise rhodium-catalyzed hydrogenation of dimethyl itaconate (Scheme 4). 

Norbornadiene- and cyclooctadiene-containing bridged olefin metathesis catalyst were also prepared by the author in the current application and are illustrated below. 

Figure 3.7. Four-electron, two-orbital interaction diagram for norbornadiene and its ionization...

In 5-47 we used the principle of conservation of orbital symmetry to explain why certain reactions take place readily and others do not. The orbital-symmetry principle can also explain why certain molecules are stable though highly strained. For example, quadricyclane and hexamethylprismane1002 are thermodynamically much less stable (because much more strained) than their corresponding isomeric dienes, norbornadiene and hexamethylbicy-clo[2.2,0]hexadiene (105).1,103 Yet the former two compounds can be kept indefinitely at... 

Figure 2. Deoxycholic acid packing illustrating the flexible size of the channel cross section. Packing viewed along the c axis (a) no guest, (b) phenanthrene, (c) norbornadiene, and (d) acetone as guests. The channels have variable size and shape depending on the mutual positions along the b axis of two adjacent bilayers. (Reproduced with permission from E. Giglio in Inclusion Compounds, Vol. 2, J. L. Atwood, J. E. D. Davies, and D. D. MacNicol, Eds., Academic Press, New York, 1984, p. 215.).

The photosensitized cyclization of norbornadiene to quadricyclane, 18, has been known for some time.270 When barralene, 19, is subjected to photosensitization, all three double bonds are involved and compound 20, which Zimmermann has named semibullvalene, results.271 Irradiation of dibenzobarralene, 21, in acetone produces the dibenzo analog of semibullvalene, 22, in high yield.272 Since there is appreciable interaction between the double bonds in both norbornadiene and barralene, these reactions may be special cases. 

The related oxobicycle (210), on photolysis in carbon tetrachloride, is converted into the isomer (211) in high yield by an intramolecular cycloaddition.186 The same transformation has been observed in norbornadiene, and other intramolecular cycloadditions are known [see, for example, Eq. (50)187]. An intermediate of this type has been postulated188 to account for the photorearrangement of 1,4-epoxy -1,4-dihydronaphthalene to benz[/]oxepin [Eq. (51)]. 

There are several cases of polycyclic triazolines, obtained by azide addition to the strained olefinic bond in bi- and tricyclic systems, that are susceptible to retro Diels-Alder reaction to yield 1-substituted triazoles. A well-established example is the monoadduct from norbornadiene and phenyl azide, which decomposes at 90-100°C to give 1-phenyltriazole and a cyclopentadiene (Scheme 138).2s 97—" 1 47 430 Similarly, the cycloadduct from the reaction of 7-oxabenzonorbornadiene and 1-azidoadamantane, when heated at 110°C, affords good yields of l-(l-adamantyl)-l,2,3-triazole in a retro Diels-Alder reaction.155... 

The monoadduct from norbornadiene and the bulky trimethylsilyl azide is less stable than the bisadduct and spontaneously yields a 1-silylated triazole that isomerizes to a 2-silyltriazole (Scheme 139).104... 

---