Chiral bis-π-allylpalladium complex catalyzed asymmetric allylation of imines:: Enhancement of the enantioselectivity and chemical yield in the presence of water
Chiral bis-π-allylpalladium complex catalyzed asymmetric allylation of imines:: Enhancement of the enantioselectivity and chemical yield in the presence of water
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DOI：
10.1021/ja037272x
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发表时间：
2003-11-19
影响因子：
15
通讯作者：
Yamamoto, Y
中科院分区：
文献类型：
--
作者：
Fernandes, RA;Stimac, A;Yamamoto, Y
由外伸亚乙基蒎烷7制备的手性π-烯丙基钯配合物2a，在1当量水存在下，以良好到高的对映选择性催化不同亚胺与烯丙基三丁基锡烷的烯丙基化反应。发现由（E）-和（Z）-7的1：1混合物制备的催化剂由1.3：1比例的两种立体异构体2a和2b组成。在分离时，2a以比2b高得多的对映体选择性催化亚胺的烯丙基化，得到相同的主要对映体，从而证明需要分离2a与2b。通过多次重结晶，我们获得了2a：2b的最高分离比>400：1。在从重结晶回收2a的过程中观察到2b异构化为2a，因为在重结晶过程中每次回收更多的2a。虽然无水THF是最好的溶剂，但我们尝试了各种添加剂，发现加入一当量的水在较短的反应时间、较高的产率和对映体选择性方面得到了最好的结果。因此，我们已经开发了一个更普遍的，可重复的，鲁棒的和非路易斯酸催化的催化不对称烯丙基化亚胺在基本上中性的条件下的程序。
The chiral pi-allylpalladium complex 2a, prepared from exoethylidenenorpinane 7, catalyzed the allylation of diverse imines with allyltributylstannane in the presence of 1 equiv of water in good to high enantioselectivities. The catalyst prepared from a 1:1 mixture of (E)- and (Z)-7 was found to be consisting of two stereoisomers 2a and 2b in 1.3:1 ratio. On separation, 2a catalyzed the allylation of imines in much higher enantioselectivities than 2b, giving the same major enantiomer and thereby justifying the need to separate 2a free of 2b. We have achieved the highest separation ratio of >400:1 for 2a:2b by repeated recrystallizations. Isomerization of 2b to 2a during recovery of 2a from the filtrates was observed as more of 2a was recovered each time during recrystallization. Although dry THF was the best solvent, we tried various additives and found that addition of one equivalent of water gave the best results with respect to shorter reaction time, higher yields and enantioselectivities. Thus, we have developed a more general, reproducible, robust and a non-Lewis acid catalyzed procedure for catalytic asymmetric allylation of imines under essentially neutral conditions.