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。