Critical profiles of chiral diether-mediated asymmetric conjugate aminolithiation of enoate with lithium amide as a key to the total synthesis of (−)-kopsinine
作者:Shingo Harada、Takeo Sakai、Kiyosei Takasu、Ken-ichi Yamada、Yasutomo Yamamoto、Kiyoshi Tomioka
DOI:10.1016/j.tet.2013.02.035
日期:2013.4
with lithium amide in toluene at −78 °C for 15 min gave, after aqueous ammonium chloride quench, the corresponding conjugate addition product with 97% ee in 89% yield. If hydrogen chloride in methanol was selected as a quencher, however, aminolithiation at −78 °C for 3 h gave the corresponding adduct with 97% ee in 54% yield, along with recovery of the starting enoate in 39% yield. Based on this finding
在-78°C条件下,在甲苯中于-78°C下用酰胺锂在丙烯中手性二醚介导的吲哚基丙酸酯与氨基酰胺的不对称氨基甲酸酯化反应,得到相应的共轭加成产物,其ee值为97%,收率为89%。但是,如果选择在甲醇中的氯化氢作为淬灭剂,则在-78°C进行3小时的氨基甲酰化反应可得到相应的加合物,其ee率为97%,收率为54%,同时回收了起始烯酸酯,收率为39%。基于在-78°C下反应不完全且反应缓慢的发现,将氨基锂化条件优化为在-60°C下放置15 h,随后在添加DMPU时用卤代烷捕获烯醇化物,得到了所需的氨基烷基化产物(98) ee百分含量为89%。通过检测不对称氨基甲硅烷基化反应,进一步实现了全合成(-)-kopsinine的方法。N-羟乙胺当量,一锅哌啶的形成,和克莱森缩合。