Harnessing Bi2S3 Nanostructure for Visible-Light-Driven Thioesterification and Amidation Reactions

Abstract

Thioester and amide are versatile functional groups commonly found in synthetic compounds, natural products, and functional materials, and they function as a crucial intermediate in organic transformations. The development of mild and efficient synthetic approaches provides a straightforward route to structurally diverse thioesters and amides, thereby enhancing the synthetic potential of carboxylic acid derivatives. This work presents a photochemical strategy for thioester and amide synthesis that employs thiobenzoic S-acids as one-electron reductants and sulfur-centred radical precursors, utilizing Bi₂S₃ nanostructures as the photocatalyst. The Bi₂S₃ nanostructures were prepared through a solvothermal method employing a choline chloride/thiourea deep eutectic solvent, which plays a multifaceted role as the solvent, soft template, and in situ sulfur source. These nanostructures were subsequently employed in visible light-induced thioesterification, enabling oxidative radical coupling of aromatic and aliphatic thioic acids with thiols under visible light. Mechanistic investigations, including TEMPO-based radical trapping experiments, confirm the involvement of free radical intermediates. Additional control experiments were conducted to elucidate the reaction mechanism and define the catalytic pathway. This protocol offers several advantages, including excellent catalytic efficiency, broad substrate applicability, high selectivity, good functional group tolerance, and catalyst recyclability, establishing it as a sustainable and practical one-pot route for thioesterification and amidation reactions.