Asymmetric α-Cyanation of β-Ketoesters Catalyzed by Chiral Tin Alkoxides

A catalytic enantioselective α-cyanation reaction of β-ketoesters with p-toluenesulfonyl cyanide (TsCN) as a cyanating reagent was achieved using an (R)-BINOL-derived chiral tin dibromide possessing 4-t-butylphenyl groups at the 3- and 3’-positions as the chiral precatalyst in the presence of sodium ethoxide in ethanol. Optically active α-cyano-β-ketoesters having a chiral quaternary carbon were obtained in good to high yields under the influence of the in situ generated chiral tin diethoxide.