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。
Preparation and regioselective reactions of novel gem-difluorinated vinyloxiranes with some organometallic reagents
作者:Takashi Yamazaki、Hisanori Ueki、Tomoya Kitazume
DOI:10.1039/b208981e
日期:2002.11.4
Hitherto unknown, relatively labile gem-difluorinated vinyloxiranes were prepared by difluoro-Wittig reactions with alpha,beta-epoxyketones; for these vinyloxiranes alkyl groups were delivered at the fluorine-attached terminal carbon atom in an SN2' manner by RLi, while Me3Al and MeMgBr-CuCl (3: 1) introduced the Me group at the allylic epoxy carbon with retention and inversion of the original stereochemistry
Reaction of gem-difluorinated vinyloxiranes with RCu(X)Li allowed us to introduce the R group regioselectively at the fluorine-attached terminal carbon atom in an SN2′ manner to afford (E)-allylic alcohols exclusively, while homoallylic alcohols with anti stereochemical relationship were found to be obtained selectively from higher-ordered cuprates derived from CuCl and RMgBr in a ratio of 1:3.
Regio- and Stereoselective Reactions of <i>g</i><i>em</i>-Difluorinated Vinyloxiranes with Heteronucleophiles
作者:Hisanori Ueki、Tomoya Kitazume
DOI:10.1021/jo051468t
日期:2005.11.1
Regio- and stereoselectivity in reactions of gem-difluorinated vinyloxiranes with heteronucleophiles were successfully controlled. Halogen atoms were introduced regioselectively at the allylic epoxide carbon with an inversion in stereochemistry using MgBr2·Et2O or Li2CuCl4 to produce anti-vic-halohydrine. The other diastereomers were obtained selectively using LiBr/AcOH or BCl3, and SN2‘ type products
宝石-二氟乙烯基环氧乙烷与杂多亲核试剂反应的区域选择性和立体选择性已得到成功控制。卤原子物在使用MgBr在立体化学的反转烯丙基环氧碳区域选择性地引入2 ·的Et 2 O或栗2的CuCl 4,以产生抗- VIC -halohydrine。使用LiBr / AcOH或BCl 3选择性地获得其他非对映异构体,并且通过改变反应温度以优异的E偏爱选择性地形成S N 2'型产物。此外,进一步的研究使我们发现区域和立体选择性S几种布朗斯台德酸的N 2'加入取决于酸的p K a值。在强酸性条件下,我们完全获得Ë烯丙醇。