Asymmetric Synthesis of α-Methylene-γ-butyrolactones Using Chiral N-Monosubstituted 2-propenamides
α-Methylene-γ-butyrolactones were prepared in high yields on treatment of N-monosubstituted 2-propenamides with aldehydes in the presence of a Lewis acid followed by acidic hydrolysis of the resulting γ-hydroxy amides.Asymmetric synthesis of α-methylene-γ-butyrolactones was investigated by using a variety of chiral 2-propenamides derived from optically active amines.Reaction of N--2-propenamide or its antipode with aldehydes in the presence of 4 equiv of TiCl4 gave, after hydrolysis, α-methylene lactones in an enantiometric excess of as high as 80percent.Optically pure 3-methylene-2-pyrrolidinones were obtained in excellent yields by a one-pot sequence starting with the γ-hydroxy amides.
