The thermal isomerization of 6-difluoromethylenebicyclo[3.2.0]hept-2-ene proceec via two competing 1,3-sigmatropic processes, with an E, nearly identical to that of the hydrocarbon. Sigmatropic isomerizations of the 6-methylenebicyclo[3.2.O]hept-2-ene system have been examined extensively by Hasselmann. 3,435 A relatively slow automerization process of lwas shown to compete with its isomerization to 3, both processes proceeding ostensibly via the bis-ally1 diradical 2. Hasselmann moreover demonstrated that the 1,3_sigmatropic process, wherein C-7 migrated to C-3, was somewhat preferred over the 3,3-process. He attributed this result to the reluctance, due to steric repulsions, of the ally1 radical to rotate through the methylene group at C-4. This argument was subsequently enhanced by his elegant study of the methylated 6-methylenebicyclo[3.2.O]hept-2-enes. 4 We would like to report, at this time, results from our investigation of the thermal izomerization of 6-difluoromethylenebicyclo[3.2.O]hept-2-ene, 4, a rearrangement which takes place exclusively via two competing 1,3-sigmatropic processes. 4 was prepared in 29% yield from bicyclo[3.2.0]hept-2-ene-6-one6 by the difluoro-Wittig process of Burton and Naae.7 It showed a characteristic intense IR absorption at 1740cm-', and gave the following NMR spectra: 'H(CCl+) 6 5.72 (S,2H), 3.72-3.16 (m,2H), 3.10-2.72 (m,lH), 2.53 (d,2H) and 2.45-2.15 (m,lH); "F(CC~I+) 6-16.6(TFA,ext)