Solvolysis with rearrangement

The Hammett cr—p correlation has proved useful in studying substituent effects of aryl-substituted systems.55 In Section 6.1 we consider applications of this linear free-energy relationship to solvolysis with rearrangement. 

These results demonstrate that, within experimental error, the corresponding reaction constants for the two reactions, solvolysis and rearrangement, are the same. In other words, the two reactions have the same dependence on substituent effects, which is consistent with Scheme 8-10 because the transition state for rearrangement is identical to the first transition state in the mechanism of solvolytic dediazoniation. 

The rearrangement of platinacyclobutanes to alkene complexes or ylide complexes is shown to involve an initial 1,3-hydride shift (a-elimina-tion), which may be preceded by skeletal isomerization. This isomerization can be used as a model for the bond shift mechanism of isomerization of alkanes by platinum metal, while the a-elimination also suggests a possible new mechanism for alkene polymerisation. New platinacyclobutanes with -CH2 0SC>2Me substituents undergo solvolysis with ring expansion to platinacyclopentane derivatives, the first examples of metallacyclobutane to metallacyclopentane ring expansion. The mechanism, which may also involve preliminary skeletal isomerization, has been elucidated by use of isotopic labelling and kinetic studies. 

In contrast to the thermal solvolysis, a rearranged enol ether 45 (and also the hydrolysis product, acetophenone) is formed in addition to the unrearranged product 44. The rearrangement is more apparent in less nucleophilic TFE. The results are best accounted for by heterolysis to give the open primary styryl cation 46 (Scheme 8). This cation gives products of substitution 44 and elimination 30 by reaction with the solvent. Alternatively, 46 can rearrange to the a-phenyl vinyl cation 47 via 1,2-hydride shift, which gives rise to 45 and 30. 

Hydrolytic studies with other K-region arene oxides 3, 20, 4, and 109 have been reported. ° ° A comparative investigation of the mechanism of the solvolysis and rearrangement of K- and non-K-region arene oxides showed that dihydrodiols were not produced from non-K-region arene oxides and the exclusively formed phenols resulted mainly from the vinylogous benzylic carbonium ions. 

The solvolysis of both cyclopropylcarbinyl and cyclobutyl derivatives proceeds with rearrangement to give mixtures of cyclopropylcarbinyl (515), cyclobutyl (516), and allylcarbinyl derivatives (517)401,402. Under certain conditions the product distributions are very similar, starting from either (57. ) or (514) (Table 16). These data... 

The [2.2.2]azabicyclic cage of the alkaloids is not immutable. The first and second cage expansions have been discovered only during the past decade. A general cinchona alkaloid solvolysis and rearrangement scheme and a unified theory have been presented. Classical solvolysis chemistry with conventional hydrocarbon substrates is complemented. The resulting azabicyclo[3.2.2]nonanes have hardly been studied. 

Esters embodying more strained ring systems did cleave during solvolysis with formation of larger rings. Thus, both epimeric 4-nitrobenzyl esters of tricyclo[3.3.1.0 ]nonan-2-ol 5 rearranged on solvolysis in aqueous acetone by cleavage of the quaternary-quaternary bond. The... 

Neopentyl (2,2-dimethylpropyl) systems are resistant to nucleophilic substitution reactions. They are primary and do not form carbocation intermediates moreover the r-butyl substituent hinders back-side displacement. The rate of reaction of neopentyl bromide with iodide ion is 470 times less than that of n-butyl bromide. Under solvolysis conditions the neopentyl system usually reacts with rearrangement to the... 

For example (Scheme 7.48), it might be supposed that in an ionizing solvent, 3-iodo-2,2-dimethylpentane, following an SnI pathway, undergoes solvolysis with loss of iodide anion and formation of secondary carbocation. Then, in a subsequent step, a 1,2-methyl shift (a Wagner-Meerwein rearrangement) from the initially... 

Several useful reviews have appeared this year. Synthesis-related reviews include the synthetic applications of selenium-stabilized carbenium ions/ the use of C-acylnitrilium ions to initiate cyclization in the synthesis of heterocycles/ and the involvement of carbocation intermediates in the cyclization of olefins with mercuric triflate. Solvolysis and rearrangement in unsaturated carbon cage compounds is reviewed/ backside r-bond assistance is suggested as being always involved." The Marcus equation is shown to be very useful in the determination of intrinsic barriers to the formation and reactions of carbocations. ... 

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