good yields. The key step of this reaction involves the ring-opening ketenylation of aziridines by the silylynolate. The reaction proceeded in a highly stereoselective manner, and ketenylation took place at the less hindered carbon. When treated with aldehydes prior to protonation, the alpha-silylated lactam enolates gave alpha-vinylidene gamma-lactams. These reactions represent a unique path to the generation