Dual Photocatalytic Pathways: Substrate-Directed Oxidative and Reductive Photocatalysis in the Presence of MoS ₂ Quantum Dots (QDs)

The growing interest in quantum dots (QDs) as catalysts for organic reactions is driven by their various properties, which are emerging as an alternative to traditional catalysts based on precious metals and small molecules. To establish their efficacy in synthetic chemistry, it is essential to demonstrate their mechanisms in diverse organic transformations. In this respect, different QDs operate via distinct mechanistic pathways, such as reductive or oxidative quenching methods. This depends on the relative redox potential of the substrate and catalyst. However, the same QD acts both ways (oxidative and reductive) in a similar reaction that was not reported earlier. In this study, we showcase the use of MoS2 QDs as a photocatalyst for the formation of differently substituted 2-aminothiazole moieties under visible light irradiation at room temperature, depending on the starting materials. In both cases, we achieved more than 80% yield, which indicates the exclusive selectivity of the mechanism. Interestingly, when derivatives of phenacyl halide were used as a substrate, we obtained a dehalogenated product, whereas 3-oxo-3-phenyl propane nitrile or a similar electron-withdrawing group (EWG)-substituted substrate yielded a product with retention of the EWG. Spectroscopic and electrochemical analyses provide valuable insights into the different charge transfer mechanisms involved in the QD-photocatalyzed synthesis of 2-aminothiazole derivatives based on the starting materials. Our methodology is scalable and suitable for derivatizations. Additionally, antibacterial studies of these derivatives highlight the pharmaceutical relevance of these moieties. This is an exclusive example of a QD-mediated organic photocatalytic transformation involving dual pathways based on the substrates.