Synthesis of new fluorinated synthons: (E and Z) ClFCCFI and (E and Z) BrFCCFI

(E)- and (Z)-1,2-difluoro-1-(trimethylsilyl)ethenes are readily prepared from trifluorovinyl(trimethyl)silane. These hydro compounds are readily metalated at low temperatures to give a stable lithium intermediate which can be captured by tri-n-butylstannyl chloride to give (E)- and (Z)-1,2-difluoro-2-trimethylsilyl-1-(tri-n-butylstannyl)ethenes. The stannyl derivatives can be halogenated stereospecifically with iodobenzene dichloride and NBS to provide the (E)- and (Z)-1-halo-1,2-difluoro-2-(trimethylsilyl)ethenes. The vinylsilanes can be readily converted in two steps to the titled synthons, (E)- and (Z)-2-halo-1,2-difluoro-1-iodoethenes by literature procedures. (E)- and (Z)-1,2-difluoro-1-(trimethylsilyl)ethenes boil ∼30 °C apart and are readily separated by fractional distillation.