2-Bicyclo octyl cation

The predominantly syn stereochemistry of the products arising from the bicyclo[3.2.1] octyl cation IV would results from the large ring strain in II, the chair conformation of which, (but not boat) facilitate the Wagner-Meerwein type rearrangement. 

Bridgehead bicyclo[4.4.0]decyl, bicyclo[4.3.0]nonyl, and bicyclo[3.3.0]octyl cations are found to be rapid equilibrating ions (see Section 3.5.2.1).188 The isomeric bridgehead congressane (diamantane) cations 52 and 53 have been prepared and observed.182 The diamant-4-yl cation 52 rapidly rearranges to the diamant-l-yl cation 53 at —60°C, possibly through intermolecular hydride shifts. Bridgehead bicyclo[3.3.3]undec-l-yl cation 54 has also been observed by 1H and 13C NMR spectroscopy.189... 

Erom the standard Gibbs energy change for the chloride exchange between tcrt-butyl and bicyclo[2.2.2]octyl cations as determined from DPA results and the appropriate leaving group corrections (at the FlP/6-31G(d) level). Entropy corrections at the HF/6-31G(d) level. Ancillary experimental data for the other species are from Tables 1 and 3. 

The bicyclo[2,2,2]octyl cation, as shown by calculations, is less stable than the 2-nor-bornyl one both in the gas phase (by about 6 kcal/mole) and in solutions At the same time the angle strain in the 2-norbomyl ion is higher, and the torsional and long-range nonbonded effects are comparable with those for the bicyclo[2,2,2]-octyl ion the difference seems to be due to the norbomyl cation geometry more favourable for a-delocalization as compared with the bicyclo[2,2,2]octyl ion. 

A useful compilation of 220 MHz n.m.r. data of substituted bicyclo[3,2,l]octan-6-ones has been published. The bicyclo[3,3,0]octyl cation appears to be implicated in the isomerization of bicyclo[3,2,l]oct-2-ene over SiOj-PaOj at 250 °C as deduced from the scrambling of label in [3- C]-tagged material and the distribution of label in the product, namely bicyclo[3,3,0]oct-2-ene. It has been found that 2,4-diphenyl-bicyclo[3,2,l]octa-2,6-diene (630) and its 6,7-dihydro-derivative undergo base-catalysed hydrogen-deuterium exchange at C-4 at essentially the same rate. Hence, the phenyl groups result in the total elimination of charge delocalization from C-4 to the C-6-C-7 double bond that is found in the unsubstituted bicyclo-octadiene. The... 

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... 

Tiecco et al. found that 4-acylp5Tidines were prone to ipso-substitution reactions with 3°— alkyl radical intermediates such as 1-adamantyl and bicyclo[2,2,2]octyl radical <76CC329>. They reasoned that the reaction began with an electron transfer from S04 to the heteroaromatic base leading to radical cation 87. Addition of Ad to C4 then gave acetate 88,... 

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)... 

The carbocation (53), formed under super-acid conditions from the phenyl-substituted tetracyclic alcohol (50), appears to be destabilized relative to (52), formed from (49) under similar conditions. Thus, for example, (53) could only be formed from (50) in FSO3H-SO2CIF at below — 100 "C, whereas (52) can be studied at — 50 °C. Above that temperature rearrangement occurs to give a pair of bicyclo-[3,3,0]octyl allylic cations. Shift data on (53) indicate that the methyl-bearing carbon aioms at the base of the pyramid are more electron deficient than their counterparts... 

Sargent, G. D., and T. J. Mason Solvolysis of 8-Vinyl-eYo-8-bicyclo[3.2.1]octyl-3,5-Dinitrobenzoate. Evidence for Stabilization by Carbon-Carbon-Hyperconjugation in the Transition State for Formation of a Tertiary Allylic Cation. J. Amer. Chem. Soc. 96, 1063 (1974). 

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