| In this paper, We synthesized three chiral phosphine-phosphoramidite ester ligands and investigated their application in iridium-catalyzed asymmetric hydrogenation of N-aryl imines.(S)-DPPNHMe124was prepared by the direct ortho-lithiation of (S)-phenethylamine, followed by diphenylphosphination. The resulting (S)-DPPNHMe124can be easily converted into the corresponding chiral phosphine-phosphoramidite ester ligands (Sc,Sa)-117by the reaction with (S)-BINOL-derived chlorophosphite.The results revealed that the introduction of groups on the naphthalene ring had an important influence on the reaction’s activity and stereoselectivity. The effect of the methyl-substitued chiral phosphine-phosphoramidite ester ligand (Sc,Sa)-117b was the best.First, this paper studied the asymmetric hydrogenation of low resistance N-aryl imines. N-(1-phenylethylidene) aniline132a was the standard substrate, the conditions of the hydroge-nation reaction has been optimized to obtain the optimal reaction conditions:0.5mol%[IR(COD)Cl]2as the metal precursor,1.1mol%methyl-substituted phosphine-phosphoramidite ester (Sc,Sa)-117b as the ligand,5.0mol%KI as the additive, dichloromethane as the solvent, under a hydrogen pressure of60bar, the reactions were carried out at room temperature for24hours. The results showed that this catalytic system has a broad substrate scope, and the hydrogenation reactions can achieve complete conversion and the best enantioselectivity (97%ee), the spatial effects and electronic effects on the benzene ring have a certain influence on the reaction.On the basis of low resistance N-aryl imines, the asymmetric hydrogenation of sterically hindered N-aryl imines was studied. The results revealed that this catalyst system also has a wide substrate scope for sterically hindered N-aryl imines. The present catalytic system features high turnover numbers and high enantioselectivity(82-98%ee) for the hydrogenation of a variety of N-aryl imines. |
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