Vinylcyclopropane- cyclopentene rearrangement mechanism, thermal

Houk, K. N., Nendel, M., Wiest, O., Storer, J. W. The Vinylcyclopropane-Cyclopentene Rearrangement A Prototype Thermal Rearrangement Involving Competing Diradical Concerted and Stepwise Mechanisms. J. Am. Chem. Soc. 1997, 119,10545-10546. 

Dinnocenzo and Conlon have described the remarkable effect of one-electron oxidation on the rate of certain vinylcyclopropane rearrangements. Exposure of several l-p-anisyl-2-vinylcyclopropane derivatives to a catalytic amount of tris(4-bromophenyl)aminium hexafluoroantimonate in acetonitrile at room temperature was found to induce ring expansion to form cyclopentenes (equation 25) temperatures in excess of 200 °C are required for the conventional thermal rearrangement cf these systems. At this time it is uncertain whether these reactions follow concerted mechanisms, or are stepwise processes involving trimethylene cation radical intermediates. 

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