Exploration of Aryllithium-Derived Copper Reagents for Quaternary-Stereogenic-Center-Forming Allylic Substitution of γ,γ-Disubstituted Secondary Allylic Picolinates
作者:Yuichi Kobayashi、Takuri Ozaki
DOI:10.1055/s-0035-1560907
日期:——
2-methyl-7-phenylhept-2-en-4-yl picolinate was reacted with phenyl copper reagents derived from phenyllithium with Cu(acac)2, Cu(OMe)2, CuBr·Me2S, and CuCN in 1–3:1 ratios in the presence of excess magnesium bromide. Although the SN2′ product with a quaternary carbon was formed, the regioselectivity was 90% at most. Instead, phenyllithium/copper(I) thiophene-2-carboxylate/magnesium bromide (Ph/Cu = 1.5–2:1, Mg/Li =
用基于芳基锂的铜试剂对 γ,γ-二取代的仲烯丙基吡啶甲酸酯(2-PyCO2H 的酯)进行烯丙基取代以构建季碳。最初,2-methyl-7-phenylhept-2-en-4-yl picolinate 与衍生自苯基锂的苯基铜试剂在 1-3 中与 Cu(acac)2、Cu(OMe)2、CuBr·Me2S 和 CuCN 反应在存在过量溴化镁的情况下比例为 1。虽然形成了带有季碳的SN2'产物,但区域选择性最多为90%。相反,发现苯基锂/铜(I)噻吩-2-羧酸盐/溴化镁(Ph/Cu = 1.5–2:1,Mg/Li = >1)可产生 >98% 的区域选择性和足够的反应性。该系统成功地使用了八种芳基锂基铜试剂,这些试剂具有空间拥挤、给电子、或吸电子取代基。抗立体化学过程是通过使用对映体富集的香叶醛衍生的吡啶甲酸酯建立的。