不对称氢化
喹啉
化学
催化作用
钌
阳离子聚合
离子液体
Noyori不对称加氢
转移加氢
二胺
组合化学
芳基
有机化学
对映选择合成
烷基
作者
Yi-Er Luo,Yan-Mei He,Qing-Hua Fan
标识
DOI:10.1002/tcr.201600095
摘要
This personal account is focused on the asymmetric hydrogenation of quinolines and their analogues recently developed by using phosphorus-free chiral cationic ruthenium(II)/η6 -arene-N-monosulfonylated diamine complexes. In our initial study, the chiral Ru-diamine complexes were found to be highly effective catalysts for the asymmetric hydrogenation of difficult quinoline substrates in room temperature ionic liquids (RTILs) with unprecedentedly excellent enantioselectivity. Our further systematic study revealed that a wide range of quinoline derivatives could be efficiently hydrogenated in alcoholic solvents, or under solvent-free and concentrated conditions with good to excellent stereoselectivity. Complexes of iridium analogues could also efficiently catalyze the asymmetric hydrogenation of quinolines in undegassed solvent. Asymmetric tandem reduction of various 2-(aroylmethyl)quinolines was achieved in high yield with excellent enantioselectivity and good diastereoselectivity. More challenging substrates, alkyl- and aryl-substituted 1,5- and 1,8-naphthyridine derivatives were successfully hydrogenated with these chiral ruthenium catalysts to give 1,2,3,4-tetrahydronaphthyridines with good to excellent enantioselectivity. Unlike the asymmetric hydrogenation of ketones, quinoline is reduced via a stepwise H+ /H- transfer process outside the coordination sphere rather than a concerted mechanism. The enantioselectivity originates from the CH/π attraction between the η6 -arene ligand in the Ru-complex and the fused phenyl ring of dihydroquinoline via a 10-membered ring transition state with the participation of TfO- anion. In addition, the Ru-catalyzed asymmetric hydrogenation of quinolines could be carried out in some environmentally benign reaction media, such as undegassed water, RTILs and oligo(ethylene glycol)s (OEGs). In the latter two cases, unique chemoselectivity and/or reactivity were observed. Catalyst recycling could also be realized by using [BMIM]PF6 and OEGs as solvents, as well as via magnetic nanoparticles. Applications of this catalytic protocol were also exemplified by the employments of the reduced products for the syntheses of some important natural alkaloids, pharmaceutical intermediates, as well as chiral diamine ligands.
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