Synthesis of Trifluoro- or Difluoromethylated Olefins by Regio- and Stereocontrolled SN2‘ Reactions of gem-Difluorinated Vinyloxiranes
摘要:
This paper presents a highly stereoselective synthesis of trifluoro- or difluoromethylated olefins via an S(N)2' type fluorination 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)center dot THF.
从容易获得的α,β-环氧酮制备了一系列迄今未知的3,4-环氧-1,1-二氟丁烯,发现这些化合物发生了区域选择性S N 2'反应,并在高度阳性时与硬RLi亲核试剂发生反应。与仅具有低区域选择性的相应非氟化乙烯基氧杂环戊烷的情况形成鲜明对比的是,带电末端具有氟的sp 2碳原子形成鲜明的对比。HMPA的加入大大改善了产物的烯属立体选择性。理论计算被用来定性地探索这些反应中选择性的性质。
β-epoxy ketones and these compounds were found to undergo regioselective SN2‘ reactions with hard RLi nucleophiles occurring at the highly positively charged terminal fluorine-possessing sp2 carbon atom in quite sharp contrast to the cases of the corresponding nonfluorinated vinyloxiranes which only attained a low level of regioselectivity. Addition of HMPA substantially improved the products' olefinic
从容易获得的α,β-环氧酮制备了一系列迄今未知的3,4-环氧-1,1-二氟丁烯,发现这些化合物发生了区域选择性S N 2'反应,并在高度阳性时与硬RLi亲核试剂发生反应。与仅具有低区域选择性的相应非氟化乙烯基氧杂环戊烷的情况形成鲜明对比的是,带电末端具有氟的sp 2碳原子形成鲜明的对比。HMPA的加入大大改善了产物的烯属立体选择性。理论计算被用来定性地探索这些反应中选择性的性质。
Synthesis of Trifluoro- or Difluoromethylated Olefins by Regio- and Stereocontrolled S<sub>N</sub>2‘ Reactions of <i>gem</i>-Difluorinated Vinyloxiranes
作者:Hisanori Ueki、Takashi Chiba、Tomoya Kitazume
DOI:10.1021/jo060089c
日期:2006.4.1
This paper presents a highly stereoselective synthesis of trifluoro- or difluoromethylated olefins via an S(N)2' type fluorination 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)center dot THF.