A Convenient Halogenation of α,β-Unsaturated Carbonyl Compounds with<i>OXONE</i>
<sup>®</sup>and Hydrohalic Acid (HBr, HCl)
作者:Kyoung-Mahn Kim、In-Hwan Park
DOI:10.1055/s-2004-831232
日期:——
Mixtures of OXONE ® and hydrobromic acid or hydrochloric acid afford solutions of bromine or chlorine, respectively. α-Bromo- or α-chloro-α,β-unsaturated carbonyl compounds were prepared by addition of hydrobromic acid or hydrochloric acid to the mixture of α,β-unsaturated carbonyl compounds and OXONE ® in CH2Cl2 followed by treatment of Et3N in moderate to good yields.
Transition metal-free diastereospecific synthesis of (Z)-2-arylidene-2,3-dihydrobenzo[b][1,4]dioxines by reaction of (Z)-1,2-dibromo-3-aryl-2-propenes with catechols
作者:Szymon P. Rekowski、Aabid A. Wani、Jürgen Conrad、Prasad V. Bharatam、Wolfgang Frey、Uwe Beifuss
DOI:10.1016/j.tet.2020.131482
日期:2020.10
A transition metal-free, diastereospecific reaction between substituted (Z)-1,2-dibromo-3-phenyl-2-propenes and substitutedcatechols using Cs2CO3 as a base at 140 °C for 18 h delivers exclusively substituted (Z)-2-arylidene-2,3-dihydrobenzo[b][1,4]dioxines in yields up to 89%. Experiments as well as quantum chemical calculations support the assumption that the one pot transformation proceeds as an
在140°C下以Cs 2 CO 3为碱在取代的(Z)-1,2-二溴-3-苯基-2-丙烯与取代的邻苯二酚之间进行的无过渡金属非对映异构反应可产生仅被取代的(Z)-2-亚芳基-2,3-二氢苯并[ b ] [1,4]二恶英的产率高达89%。实验以及量子化学计算均支持以下假设:一锅转化以分子间O-烯丙基化/分子内O-乙烯基化的方式进行。
Stereoselective Halo-Succinimide Facilitated α-Halogenations of Substituted α-Trialkylsilyl-β-Substituted-α,β-Unsaturated Esters
作者:Kristina C. Probasco、Michael P. Jennings
DOI:10.1021/acs.joc.1c00876
日期:2021.7.2
halogenation of a series of (E)-α-trimethylsilyl-β-alkyl(aryl)-α,β-unsaturated esters in dimethylformamide (DMF) has furnished (Z)-β-substituted-α-halogenated-α,β-unsaturated ester products in moderate to high isolated yields (58–90%) with dr values of >20:1 coupled with the inversion of olefin stereochemistry. The reaction process was hypothesized to include an initial halonium cation intermediate,
NXS (X = Cl, Br) 介导的一系列 ( E )-α-三甲基甲硅烷基-β-烷基(芳基)-α,β-不饱和酯在二甲基甲酰胺 (DMF) 中的卤化提供了 ( Z )-β-取代-α-卤代-α,β-不饱和酯产物的分离产率中等至高(58-90%),dr 值大于 20:1,并伴有烯烃立体化学的反转。假设反应过程包括最初的卤阳离子中间体,然后是区域选择性的 DMF 开环。随后的抗-E2-型伴随消除允许产物乙烯基溴和氯酯的立体选择性形成。
NAD(P)<sup>+</sup>–NAD(P)H Model. 54. Free Radical Mechanism for the Reductive Debromination of<i>vic</i>-Dibromides to Alkenes
作者:Shinro Yasui、Kaoru Nakamura、Atsuyoshi Ohno
DOI:10.1246/bcsj.58.1847
日期:1985.6
vic-Dibromides undergo reductive debromination with a model of NAD(P)H, N-benzyl-1,4-dihydronicotinamide, to afford the corresponding alkenes quantitatively. Stereochemistry of the reduction suggests that the reaction involves a free radical intermediacy.
in CH2Cl2 followed by the addition of an alcohol in the presence of manganese dioxide under ultrasonic irradiation constitutes a stereoselective one-pot procedure for the preparation of Z-configured α–bromo-α,β-unsaturatedesters in good to excellent yield.