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  • Title: Catalytic asymmetric synthesis of 3-(alpha-hydroxy-beta-carbonyl) oxindoles by a Sc(III)-catalyzed direct aldol-type reaction.
    Author: Shen K, Liu X, Zheng K, Li W, Hu X, Lin L, Feng X.
    Journal: Chemistry; 2010 Mar 22; 16(12):3736-42. PubMed ID: 20175165.
    Abstract:
    A direct catalytic asymmetric aldol-type reaction of 3-substituted-2-oxindoles with glyoxal derivatives and ethyl trifluoropyruvate, catalyzed by a chiral N,N'-dioxide-Sc(OTf)(3) (Tf = trifluoromethanesulfonyl) complex, has been developed that tolerates a wide range of substrates. The reaction proceeds in good yields and excellent enantioselectivities (up to 93% yield, 99:1 diastereomeric ratio (dr), and >99% enantiomeric excess (ee)) under mild conditions, to deliver 3-(alpha-hydroxy-beta-carbonyl) oxindoles with vicinal quaternary-tertiary or quaternary-quaternary stereocenters. Even with 1 mol % catalyst loading or on scaleup (10 mmol of starting material), maintenance of ee was observed, which showed the potential value of the catalyst system. In studies probing the reaction mechanism, a positive nonlinear effect was observed and Sc(III)-based enolate intermediates were detected by using ESIMS. On the basis of the experimental results and previous reports, a possible catalytic cycle was assumed.
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