Concise Brønsted Acid-catalyzed Synthesis of Multi-substituted γ-Benzo- (Thio)Pyrones

Introduction: In this study, we report the Brønsted acid-catalyzed synthesis of multisubstituted γ-benzo (thio)pyrones. Both multi-substituted γ-benzopyrones and 4H-1- benzothiopyran-4-ones can be concisely synthesized by directly using o-hydroxybenzoylacetones or substituted thiophenols as starting materials. Methods: Compounds 2a-2p were synthesized by 1,3-aryldi-ketones mixed with MeOH/HCl at 65 °C for 4 h and 4a-4e were synthesized by thiophenol and ethyl acetoacetate mixed with PPA at 160 °C for 5 h. All these obtained compounds were characterized by NMR or HR-MS. Results: A series of γ-benzo(thio)pyrone compounds can be synthesized via a mild procedure under the catalyst of Brønsted acid (HCl or PPA). Discussion: This synthesis method based on Brønsted acid catalysis has good substrate scope. The reaction mechanism has been verified by density functional theory calculations. Conclusion: This method aligns with the principles of green chemistry, offers a valuable reference for the synthesis of multi-substituted γ-benzo(thio)pyrones, and broadens the applicability of Brønsted acid-catalyzed green synthesis.