Palladium-Catalyzed [5 + 4] Cycloaddition of 4-Vinyl-4-Butyrolactones with N -Tosyl Azadienes: Construction of Nine-Membered Ring.

In this paper, we reported the palladium-catalyzed formal [5 + 4] cycloaddition reactions between 4-vinyl-4-butyrolactones (VBLs) and azadienes. Under mild reaction conditions, a wide range of benzofuran-fused 9-membered heterocyclic compounds had been provided in moderate to excellent yields with exclusive regioselectivities and excellent diastereoselectivities. The practical applicability of the synthesis was demonstrated through scale-up reaction and further transformation.