Synthesis of Trifluoro- or Difluoromethylated Olefins by Regio- and Stereocontrolled S_N2' Reactions of gem-Difluorinated Vinyloxiranes

摘要

This paper presents a highly stereoselective synthesis of trifluoro- or difluoromethylated olefins via an S_N2' type fiuorination or reductions of gem-difluorinated vinyloxiranes.Their fluorination with HF-Py furnished trifluoromethylated allylic alcohols with exclusive E selectivity.On the other hand,their reduction with DIBAL-H afforded difluoromethylated E-allylic alcohols predominantly,whereas the corresponding Z isomers were formed exclusively by treatment with BH_3 centre dot THF.