A doubly destabilized antiaromatic cyclopentadienyl cation: solvolysis of a 5-trifluoroacetoxy-5-heptafluoropropyl 1,3-cyclopentadiene.
The 5-trifluoroacetoxy-5-heptafluoropropylcyclopentadiene 15 rearranges to the isomeric trifluoroacetate 16 with a rate constant 5 x 10(5) less than that for solvolysis of the corresponding 5-CH(3) derivative 5. Labeling of 15 with (18)O shows the rearrangement occurs by a [1,5]-sigmatropic rearrangement. Solvolysis of 16 occurs at a rate 4 times slower than its formation from 15 and leads to the extensively rearranged fulvene 18, implicating formation of the doubly destabilized cation 20. Carbocation formation from 15 is retarded by a factor of 10(20) relative to the model 11, showing cumulative destabilizing effects due to formation of the antiaromatic cyclopentadienyl carbocation and electron withdrawal by the fluoroalkyl group.
Allen
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Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6 Canada.
Tidwell
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TT