Synthesis of highly-strained gem-difluoro compounds by reaction of difluoromethylene with cycloalkenes

Trans-Cyclooctene is thought to be more reactive than cis-cyclooctene due to its trans-structure. When cis or trans-clooctene reacts with difluormethylene (:CF2), trans-9,9-difluorobicyclo[ 6,1,0] nonane was generated in much higher yield than cis-9,9-difluorobicyclo[6,1,0]nonane. [PhCF3P+CF2Br]Br- was chosen to be the difluoromethylene precursor in this study. The reason was that the reaction condition for trans-cyclooctene and :CF2 should be at low temperature. Only [PhCF3P+CF2Br]Br- could generate CF2 at lower temperature (e.g. room temperature). We succeeded in the synthesis of trans-9,9-difluorobicyclo[6,1,0]nonane and its cis isomer and have demonstrated a principle of CF2 reactivity