Bicyclooctyl Cations

The nonclassical ion 158 in contrast to the 2-norbomyl cation 5 has no plane of symmetry and so, if formed from an optically active precursor it gives rise solely to optically active products. 

The cl ical bicyclo[2,2,2]octyl ion 159, unlike classical 2-norbomyl ion 6, has a symmetry plane so that products derived from it must be racemic. 

The skeletal rearrangements occurring via an intermediate nonclassical ion 158 are readily detected since they lead to a different, bicyclo[3,2,l]octyl system (cf. with the rearrangement of norbomyl derivatives to norbomyl ones). 

The stereochemical interaction of the classical ion 159 with the solvent should not be determined by the ion geometry since it is symmetrical. The participation of the solvent and the shielding by the leaving group should lead to some net inversion of the configuration if the solvolysis proceeds via the classical ion 159. 

The acetolysis of optically active brosylate 157 results in an optically active bicyclo[2,2,2]acetate 160 with 85 15% retention of configuration the second product — the axial 2-bicyclo[3,2,l]octyl acetate 161 (63 35) — turned out to be optically active as well. Not even any traces were found of the more stable equatorial isomer 162. From these data the authors concluded an intervention of the nonclassical ion 158. The degree of retention (85 15%), however, does not preclude the classical ion 159 to play a minor role as well. 

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Bicyclooctyl Cations. Solvolyses of endo-2-bicyclo[3.2.1]octyl tosylate (73)55S and 4-cycloheptenylcarbinyl brosylate (4< 7)377 555 give similar product mixtures consisting primarily of endo-2-bicyclo [3.2.1] octanol or its acetate (819)... 

Bicycloheptyl, Bicyclohexyl, and Bicyclooctyl Cations 4.1 Hie fficyclo/2,2,l/hexyI Cation... 

Olah and Liang were able to establish by means of H NMR studies in superacidic solutions at —78 °C that all bicyclooctyl systems rearrange to the [3.3.0] cation 296 (Scheme 46).311 When 296 was allowed to warm to 0 °C, it rearranged irreversibly to the 2-methylnorbomyl cation. 

Entries 6-9 and 10-12 illustrate the tendency for rearrangements to occur leading to the most stable cation in each particular system. The tertiary 1-methylcyclopentyl cation is the only ion observed from a variety of precursors containing five- and six-membered rings. The tertiary bicyclo[3.3.0]octyl cation is formed from all bicyclooctyl precursors. As previously mentioned, the tendency to rearrange to thermodynamically stable ions by multiple migrations is a consequence... 

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