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  • Title: Asymmetric cyclopropanation of β,γ-unsaturated α-ketoesters with stabilized sulfur ylides catalyzed by C2-symmetric ureas.
    Author: Cheng Y, An J, Lu LQ, Luo L, Wang ZY, Chen JR, Xiao WJ.
    Journal: J Org Chem; 2011 Jan 07; 76(1):281-4. PubMed ID: 21141872.
    Abstract:
    A novel organocatalytic asymmetric cyclopropanation of β,γ-unsaturated α-ketoesters with stabilized sulfur ylides using C(2)-symmetric urea as a hydrogen-bond catalyst has been described. This reaction allows an efficient access to 1,2,3-trisubstituted cyclopropane derivatives in moderate to good yields with up to 16:1 dr and 90:10 er under mild reaction conditions. The mechanism study proved that the high stereoinduction originated from the cooperative effect of the hydrogen-bond catalyst.
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