Cyclopropyl-substituted derivatives solvolysis

Finally, de Meijere and coworkers ° have studied the reactivities of some bridgehead substituted trishomobarrelene and trishomobullvalene derivatives. These are triscyclopropylcarbinyl systems. The relative rates of solvolysis below are for reactions in 80% aqueous dioxane at 25°C . In both systems the cyclopropyl substitution results in... 

A number of values for substituted cyclopropyl groups have also been derived from solvolysis reactions, as shown in Table 5, along with one value from aromatic detritiation. ... 

An essentially additive effect of ring substituents on the 7r-donor ability of cyclopropyl in generation of carbocation derivatives was also shown in the solvolysis of a series of methyl-substituted cyclopropylcarbinyl dinitrobenzoates (ODNB) (equation 4) studied by... 

It was observed that the rate of solvolysis of the 2,2-dimethyl derivative 17a was accelerated by a factor of 12 relative to the unsubstituted derivative 17b in 90 % acetone at 25 °C, whereas the 2,2-dichloro analog 17c was 1.4 x 10 times less reactive than 17b . These rate effects are consistent with the <7p constants for such substituted cyclopropyl groups discussed above. 

The general recognition of the difference between the 4/3 + 2 and 4/3 r-systems led to many studies of the cyclopentadienyl cation. In an early observation, Breslow et al. reported that cyclopentadienyl halides are remarkably resistant to solvolysis. Thus, cyclopentadienyl iodide does not react with silver perchlorate in propionic acid solution. Subsequently, it has been possible to prepare substituted cyclopentadienyl derivatives which undergo solvolysis, but the rates of reaction are very low. ° Cyclopropyl substituents appear to be particularly effective in stabilizing the cation. ... 

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