Asymmetric Cyclopropanation of β,γ-Unsaturated α-Ketoesters with Stabilized Sulfur Ylides Catalyzed by C2-Symmetric Ureas

A novel organocatalytic asymmetric cyclopropanation of β,γ-unsaturated α-ketoesters with stabilized sulfur ylides using C2-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.