The stereospecific preparation of (E)-1,2-difluoro-1,2-disubstituted alkenes

(Z)-1,2-difluoro-2-substituted vinyl silanes were prepared stereospecifically from chlorotrifluoroethene, chlorotrimethylsilane and alkyl or aryllithium reagents. Subsequent exchange of the trimethylsilyl group via reaction of the vinylsilane with KF/n-Bu3SnCl/DMF stereospecifically afforded the corresponding (Z)-1,2-difluoro-2-substituted vinyl stannanes. Pd(PPh3)4/Cu(I)I/DMF coupling of the vinyl stannanes with substituted aromatic iodides stereospecifically provided the (E)-1,2-difluoro-1-substituted aryl-alkenes in excellent yield.