S<sub>N</sub>2’ versus S<sub>N</sub>2 Reactivity: Control of Regioselectivity in Conversions of Baylis-Hillman Adducts
作者:Mahiuddin Baidya、Grygoriy Y. Remennikov、Peter Mayer、Herbert Mayr
DOI:10.1002/chem.200902487
日期:2010.1.25
is used, a second SN2’ reaction converts 8 into their thermodynamically more stable allyl isomers 9. The second‐order rate constants for the reactions of 6 with carbanions have been determined photometrically in DMSO. With these rate constants and the previously reported nucleophile‐specific parameters N and s for the stabilized carbanions, the correlation log k (20 °C)=s(N + E) allowed us to calculate
TiCl 4诱导的α,β-不饱和羰基化合物与醛的Baylis-Hillman反应产生(Z)-2-(氯甲基)乙烯基羰基化合物5,该化合物与1,4-二氮杂双环[2.2.2]辛烷(DABCO ),奎尼丁和吡啶,得到烯丙基铵离子6。将它们与少于一当量的稳定化碳负离子的钾盐(例如丙二酸酯)结合,可在动力学控制的条件下(S N 2'反应)生成亚甲基衍生物8。当使用多于一个当量的碳负离子时,第二个S N 2'反应将8转化为其热力学更稳定的烯丙基异构体9。已在DMSO中以光度法确定了6与碳负离子反应的二级速率常数。利用这些速率常数和先前报道的稳定化碳负离子的亲核试剂特定参数N和s,相关性对数k(20°C)= s(N + E)使我们能够计算出烯丙基铵离子6的亲电参数E( -19 < E <−18)。动力学数据表明,S N 2'反应通过加速率消除加成消除机理进行。
Amine and Titanium (IV) Chloride, Boron (III) Chloride or Zirconium (IV) Chloride-Promoted Baylis-Hillman Reactions
作者:Min Shi、Jian-Kang Jiang、Shi-Cong Cui
DOI:10.3390/61100852
日期:——
Baylis-Hillman reactions of various aryl aldehydes with methyl vinyl ketone at temperatures below -20oC using Lewis acids such as titanium (IV) chloride, boron (III) chloride or zirconium (IV) chloride in the presence of a catalytic amount of selected amines used as a Lewis bases afford the chlorinated compounds 1 as the major product in very high yields. Acrylonitrile can also undergo the same reaction to give
Titanium(IV) chloride, zirconium(IV) chloride or boron trichloride and phosphine-promoted Baylis–Hillman reaction of aldehydes with α,β-unsaturated ketone
In the Baylis–Hillman reaction of aldehydes with an α,β-unsaturated ketone, the chlorinated compound 1 was obtained as the major product using tributylphosphine as a Lewis base in the presence of titanium(IV) chloride, zirconium(IV) chloride or borontrichloride in dichloromethane at <−20 °C. A plausible reaction mechanism has been proposed. Using (R)-(+)-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl
Amendment in Titanium(IV) Chloride and Chalcogenide-Promoted Baylis–Hillman Reaction of Aldehydes with α,β-Unsaturated Ketones
作者:Min Shi、Jian-Kang Jiang
DOI:10.1016/s0040-4020(00)00384-7
日期:2000.6
The Baylis–Hillman reaction can be drastically affected by the reaction temperature and Lewis base. When the reaction was carried out at <−20°C using methyl sulfide as a Lewis base in the presence of titanium(IV) chloride, the chlorinated compound 1 was obtained as the major product. However, if the reaction was carried out at room temperature (10°C) in the presence of titanium(IV) chloride, the elimination
Enantiodivergence in the reduction of α-methyl and α-halomethyl enones by microorganisms
作者:Bruno R.S. de Paula、Dávila S. Zampieri、J. Augusto R. Rodrigues、Paulo J.S. Moran
DOI:10.1016/j.tetasy.2013.07.007
日期:2013.9
Enones (Z)-3-methyl-(Z)-3-chloromethyl- and (Z)-3-bromomethyl-4-R-3-buten-2-one (R = n-pentyl, phenyl, 2'- and 4'-chlorophenyl, 3'- and 4'-nitrophenyl, 4'-methoxyphenyl) were synthesized and subjected to reduction by the microorganisms Saccharomyces cerevisiae and Geotrichum candidum. Whereas the bioreduction of 3-methy-4-R-3-buten-2-ones afforded the corresponding (S)-4-R-3-methybutan-2-ones, the bioreduction of 3-chloromethyl- and 3-bromomethyl-4-R-3-buten-2-ones afforded the corresponding (R)-4-R-3-methybutan-2-ones. (C) 2013 Elsevier Ltd. All rights reserved.