Lewis Acid-Mediated Reactions of Alkyl Azides with α,β-Unsaturated Ketones

Alkyl azides react with saturated ketones upon treatment with Lewis acids to afford ring-expansion products through the azido-Schmidt reaction, but this reaction does not proceed when α,β-unsaturated ketones are used. In this study, alkyl azides were reacted with enones in the presence of Lewis acids to give enaminones (vinylogous amides), which formally involve a ring contraction reaction. The mechanism and scope of this reaction is discussed.