Construction of Nine‐Membered Heterocycles through Palladium‐Catalyzed Formal [5+4] Cycloaddition

The first catalytic formal [5+4] cycloaddition to prepare nine‐membered heterocycles is presented. Under palladium catalysis, the reaction of N‐tosyl azadienes and substituted vinylethylene carbonates (VECs) proceeds smoothly to produce benzofuran‐fused heterocycles in uniformly high efficiency. Highly diastereoselective functionalization of the nine‐membered heterocycles through peripheral attack is also demonstrated. On cloud nine: The first catalytic formal [5+4] cycloaddition is presented for the preparation of nine‐membered heterocycles. Under palladium catalysis, the reaction of N‐tosyl azadienes and substituted vinylethylene carbonates (VECs) proceeds smoothly to produce the benzofuran‐fused heterocycles with uniformly high efficiency. Highly diastereoselective functionalization of the nine‐membered heterocycles through peripheral attack is also demonstrated.