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Asymmetric Glyoxylate-Ene Reactions Catalyzed by Chiral Pd(II) Complexes in the Ionic Liquid [bmim][PF6]

Author(s): Xi Jun He | Zhen Lu Shen | Wei Min Mo | Bao Xiang Hu | Nan Sun

Journal: International Journal of Molecular Sciences
ISSN 1422-0067

Volume: 8;
Issue: 6;
Start page: 553;
Date: 2007;
Original page

Keywords: Ionic liquid | glyoxylate-ene reaction | palladium | chiral | 1-n-butyl-3-methyl- imidazolium hexafluorophosphate

The room temperature ionic liquid [bmim][PF6] was employed as the reactionmedium in the asymmetric glyoxylate-ene reaction of α-methyl styrene (4a) with ethylglyoxylate using chiral palladium(II) complexes as the catalysts. [Pd(S-BINAP)(3,5-CF3-PhCN)2](SbF6)2 (1b) showed the highest catalytic activity. Under the reaction conditionsof 40 oC, 0.5 h, and 1b/4a molar ratio of 0.05, ethyl α-hydroxy-4-phenyl-4-pentenoate wasobtained in excellent chemical yield (94 %) with high enantioselectivity (70 %). Otherα-hydroxy esters can also be obtained in high chemical yields and enantioselectitiesthrough the glyoxylate-ene reactions of alkenes with glyoxylates catalyzed by 1b in[bmim][PF6]. Moreover, the ionic liquid [bmim][PF6] which contained the palladium(II)complex could be recycled and reused several times without significant loss of the catalyticactivity.
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