N-Heterocyclic Carbene-Catalyzed [4 + 2] Annulation of Enolizable Thioesters for the Synthesis of 2-Pyrones

An N-heterocyclic carbene (NHC)-catalyzed [4 + 2] annulation enables the direct synthesis of 2-pyrones from α-chlorothioesters and β,γ-unsaturated α-keto esters or chalcones. The method utilizes NHC-activated α-chlorothioesters to generate key intermediates for 2-pyrone formation with high functional group tolerance. Moreover, the 2-pyrones were transformed into polysubstituted benzene and naphthalene derivatives, showcasing their synthetic value.