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.

Graphical abstract. (Z)-(2-substituted-1,2-difluoroethenyl)silanes can be stereospecifically prepared in a one pot reaction sequence starting from chlorotrifluoroethene. Subsequent treatment of these vinyl silanes with either n-Bu3SnCl/KF/DMF/80 °C or (n-Bu2Sn)2O/cat. KF/DMF/80 °C stereospecifically provide the corresponding (Z)-monosubstituted vinyl stannanes. Coupling of the (Z)-vinylstannanes with aryliodides using Pd(PPh3)4/Cu(I)I catalysis in DMF at RT provides excellent yields of the (E)-1,2-difluoro-1,2-disubstituted alkenes.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Stereospecific synthesis of (E)-1,2-difluoro-1-substituted aryl-alkene. ► Stereospecific synthesis of (Z)-RCFCFSnBu3. ► Stereospecific Si/Sn exchange of (Z)-1,2-difluoro-2-substituted vinylsilanes. ► Preparation of (Z)-1,2-disubstituted vinyl silanes from F2CCFCl.