Bicyclo hexenyl cations rearrangement

The walk rearrangement in the parent bicyclo[3.1.0]hexenyl cation was examined by using deuterium labels at C-2 and C-6 (113). 

The photochemical conversion of the protonated isodurene into a respective bicyclo[3.1.0]hexenyl cation ended in failure . An attempt to generate this ion indirectly has shown it to be unstable (since it contains a CH3 group only at one end of the enylic fragment) and to rajndly undergo reverse rearrangement. 

For the non-substituted bicyclo[3.1.0]hexenyl cation the degenerate rearrangement proceeds far more slowly and it could only be observed by labeled atoms The quantum chemical analysis of this process is made in Another rearrangement of bicyclo[3.1.0]hexenyl cations is the C,—C5 bond rupture to the benzenium ions 254-256.277,767.771.774,. 

Hexamethyl-Dewar-benzene reacts with sulphur dioxide, in presence of antimony pentafluoride, to give the bicyclo[2,l,l]hexenyl cation (344) which was identified by its and n.m.r. spectra. Quenching of the ion with wator or methoxide gives the tricyclic sulphone (345) and hexamethylbenzene. The sulphone could have been formed by rearrangement of the bicyclo[2,l,l]hexenyl cation to the bicyclo-[3,l,0]hexenyl cation (346). 

Based on ab initio SCF calculations (114), the difference in the activation energies required for the two walk rearrangements might result entirely from these ground state differences between the bicyclo-[3.1.0]hexenyl and homotropylium cations. 

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