Ring-Opening Rearrangements of Sesquinorbornyl Cations

Article abstract of DOI:10.1021/jo00385a036

In superacid media, anti-sesquinorbornene (2) is protonated to yield the directly related carbocation 2⁺ at -78 deg C.On raising the temperature the cation rearranges irreversibly with ring opening to the 1-(2-norbornyl)-2-cyclopentenyl allylic cation 3⁺.This rearrangement does not occur with syn-sesquinorbornene, within the temperature range studied, but is observed in the syn isomer 7 whose double bond is not shared between the norbornene ring systems.These observations permit the formulation of a general mechanism for the formation of the allylic cation.