Synthesis of Nine-Membered Azlactones by Palladium-Catalyzed Ring-Expansion of γ-Methylidene-δ-valerolactones with Aziridines

A palladium-catalyzed formal [6 + 3] cyclization of γ-methylidene-δ-valerolactones with aziridines has been developed to produce 1,4-oxazonan-9-ones, a class of nine-membered azlactones that are not easily accessible by existing methods. The products thus obtained can also be further functionalized with ease.