Synthesis of γ-Thiapyrones by Diels-Alder/Retro-Diels-Alder Reaction of α-Pyrones with 5-H-1,2,3-Thiadiazoles

The efficient synthesis of gamma-thiapyrones by a base-mediated Diels-Alder/retro-Diels-Alder reaction of alpha-pyrones with 5-H-1,2,3-thiadiazoles is reported herein. Thioketenes in situ generated from thiadiazoles as electron-poor dienophile and electron-rich 4-hydroxy-2-pyrones as dienes are conjunctively transformed into a series of gamma-thiapyrones with broad functional group compatibility in good to excellent yields (35 examples, 67% average yield).