Ligand design for dual enantioselective control in Cu-catalyzed asymmetric conjugate addition of R2Zn to cyclic enone
作者:Misato Yoshimura、Naoatsu Shibata、Miaki Kawakami、Satoshi Sakaguchi
DOI:10.1016/j.tet.2011.04.028
日期:2012.4
15, which was derived from (S)-tert-leucinol, produced (S)-18 in preference to (R)-18. A series of azolium salts were synthesized from (S)-serine esters, and the reaction conditions for the ECA reaction were optimized to produce (R)-18 with 69% ee. The best results were obtained in the case of the reaction of 4,4-dimethyl-2-cyclohexen-1-one (34) with Et2Zn catalyzed by Cu(OTf)2 in combination with azolium
设计并合成了一种新的手性N-杂环卡宾(NHC)配体,该配体衍生自天然α-氨基酯。的耦合Ñ -methylbenzimidazole与α氯乙酰胺衍生物,将其从氯乙酰氯和(制备小号) -丝氨酸甲酯,得到相应的酯/酰胺官能化的氮鎓化合物20。2-环己烯-1-酮(17)与Et 2 Zn在催化量的Cu(OTf)2和20存在下的反应生成了(R)-3-乙基环己酮(18)作为主要产品。相反,在衍生自(S)-叔亮氨酸的羟基酰胺官能化的偶氮化合物15的作用下,由Cu(OTf)2催化的对映选择性共轭加成(ECA)反应产生了(S)-18优先(R)-18。由(S)-丝氨酸酯合成了一系列的偶氮盐,优化了ECA反应的反应条件以产生具有69%ee的(R)-18。在4,4-二甲基-2-环己烯-1-酮(34),以及由Cu(OTf)2和偶氮化合物催化的Et 2 Zn 。当34与Et 2 Zn的反应在催化量的Cu(OTf)2和2