Bicyclo octadienes formation

A number of CSl additions have been shown to produce much less stable j5-lactams. The azetidinone (51) was isolated from the reaction of cyclo-hexadiene with CSI for five minutes at room temperature, while after thirty hours (52) was formed, and the reaction in refluxing chloroform gave (53). Analogous reactions with bicyclo-octadiene did not involve the tautomeric cyclo-octatriene. Initial formation of a 1,4-dipolar intermediate was... 

Other examples of favored formation of cyclobutanes include photocycloadditions of tri-fluoromethyl-substituted coumarins with dienes,and of 5-(trifluoromethyl)-l,3-dioxin-4-ones, e.g. 3, with alkenes, " - - " as well as intramolecular photocycloadditions, such as those of bicyclo[2.2.2]octadiene and tricyclononadiene derivatives. 

In contrast to norbornadiene, bicyclo[2.2.2]octa-2,5-diene does not always give the transan-nularly bridged products in normal solution reactions, whereas in the anodic electrooxidation this nonconjugated octadiene showed the formation of products, mainly tricyclo-[2.2.2.0 ]octane derivatives 5 and 6 from transannular interaction, exclusively. ... 

Fig. 15 [4+2] Cycloaddition reactions of r -anisole complexes via a 4H-anisolium intermediate and the formation of various bicyclo[2.2.2]octadiene and bicyclo[2.2.2.]octatriene complexes...

As noted above, the skeletal rearrangements in the 8, 1 reactions and the stereospecificity in the formation of reaction products are essential criteria of the intermediate formation of nonclassical ions. Nevertheless the results obtained can be explained by assuming the C—J bond ionization to proved with a simultaneous shift of the a-bond C —C in the isomer 350 and of the a-bond C —C in the compound 351. The structures 347 and 348 must be transition states of ionization processes. The authors of , however, consider this assumption less probable because the synchronous process in question is a reaction of the 8, 2 type at the bridged carbon atom and for the bridged atoms of rigid bicyclic systems such processes are known to be strongly hindered. The formation of ion 318 with bicyclo[3,2,I]octadiene skeleton consecutively from ion 347 rather than directly from compound 350 with the geometry of bicyclo[2,2,2]octadiene is also in fuller accordance with the principle of so-called least motion " 29)... 

The formation of the bicyclo[3.2.1]octadienes in Table 1 in such high yields implies that the cyclopropanation step occurs with very high diasteroselectivity because only cis- divinylcyclopropanes are expected to undergo a Cope rearrangement under the mild reaction conditions. Such stereoselectivity is very unusual in the carbenoid... 

Metal-catalysed Isomerizations. The formation of 7r-allylchloropalladium(ii) complexes from a series of cyclopropenes proceeds with symmetrical complexation of the metal to the 7i-bond, and not a-bond cleavage, as the rate-determining step. With substituted cyclopropenes containing a phenyl group at C-3, the it-allyl complex rearranges to indenyl complex either spontaneously or on treatment with triphenyl-phosphine. trans-Chloropalladation of bicyclo[5,l,0]oct-3-ene has been described, and the complex decomposes not to cyclo-octadiene complex, but to a cyclo-octene n-allyl system. ... 

Ikeda, H., Takasaki, T., Takahashi, Y, Konno, A., Matsumoto, M., Hoshi, Y, Aoki, T., Suzuki, T, Goodman, J., and Miyashi, T, Photoinduced electron-transfer Cope rearrangements of 3,6-diaryl-2,6-octadienes and 2,5-diaryl-3,4-dimethyl-l,5-hexadienes stereospecificity and an unexpected formation of the bicyclo[2.2.0]hexane derivatives,/. Org. Chem., 64,1640, 1999. 

---