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The photochemical isomerization of trans and cis-difluorostilbenes has been studied.In the presence of a photosensitizer (biacetyl, 0.05 mol·L~(-1)) about 75％ of the trans form can beconverted into the crystalline cis form. The reactions of difluorocarbene (CF_2) from the Seyferthreagent (PhHgCF_3) with cis- and trans-stilbene obey the Skell rule, i. e., stereospecific cycloaddition.However, although the reaction of CF_2 with trans-1,2-difluorostilbene yields trans-1,2-diphenyl-perfluorocyclopropane (9) as the only isolable product, the reaction of CF_2 with cis-difluorostilbenealso gives the same trans-cycloadduct as the only isolable Product. A possible mechanistic path in-volving the homolytic cleavage of the highly activated cyclopropane C-C bond facing the CF_2 groupis discussed.
The photochemical isomerization of trans and cis-difluorostilbenes has been studied. The presence of a photosensitizer (biacetyl, 0.05 mol·L -1) about 75% of the trans form can be converted into the crystalline cis form. The reactions of difluorocarbene (CF_2) from the Seyferthreagent (PhHgCF_3) with cis- and trans-stilbene obey the Skell rule, ie, stereospecific cycloaddition. Despite, the reaction of CF_2 with trans-1,2-difluorostilbene yields trans-1,2-diphenyl -perfluorocyclopropane (9) as the only isolable product, the reaction of CF_2 with cis-difluorostilbenealso gives the same trans-cycloadduct as the only isolable Product. A possible mechanistic path in-volving the homolytic cleavage of the highly activated cyclopropane CC bond facing the CF_2 groupis discussed.