Electron deficient dienes 3 and 4 are obtained by defluorination of perfluo
robicyclo-butylidene (1) and -pentylidene (2), using tetrakis(dimethylamino
)ethene (TDAE), and these dienes are very reactive. With alkali metal fluor
ides, 4 gave a stable observable anion while 3 gave oligomers. The correspo
nding fluorinated allyl anion was however obtained via 3 in the presence of
TDAE. Further reactions of 3 and 4 are described.