Introduction
Photocatalyst plays a very important role in organic photochemistry. The catalyst has aroused great interest of chemists as it offers a powerful tool to organic synthesis. More and more transition-metal complexes have been proved to catalyze light-driven organic reactions. These photocatalysts can be excited in the wavelength range of visible light and have higher efficiency for light absorption than organic small molecules. Photocatalysts used in organic synthesis are mainly divided into transition metal complex photocatalysts and metal-free organic photocatalysts. Among them, acridine, carbazole, ruthenium and iridium photocatalysts have redox activities and have been widely used in photocatalysis. In addition, other photocatalysts also showed good photocatalytic activities.
Typical Product: Eosin Y
Eosin Y, as a cheaper metal-free dye, refers to the 2',4',5',7'-tetrabromo derivative of fluorescein, has been most widely employed. A large number of mechanistic studies have been carried out on the reactions of organometallic photocatalysts, and the oxidative quenching pathway of eosin Y-catalyzed reactions has mostly been interpreted as similar to the related [Ru(bpy)3Cl2]-catalyzed reactions. The catalytic mechanism is also similar to that of ruthenium. Take arene diazonium salts as an example, the reaction mechanism of eosin Y-catalyzed substitutions is shown in the Figure 1[1].
Fig.1 Chemical structure of eosin Y and proposed general reaction mechanism[1]
Applications of Eosin Y
- Activation of carbon-carbon triple bonds
The synergistic merger of eosin Y and Cu(OTF)2 is employed to achieve the bond-forming reaction of alkynes with weakly nucleophilic reagents and it is an efficient reaction for arene-ynes. Alkynes have been widely used in organic synthesis, and copper can activate the C-C triple bond as an efficient Lewis acid catalyst. However, copper does not have sufficient Lewis acidity for the typical weakly nucleophilic reagents, so the photocatalyst eosin Y and lewis acid copper salts are combined to form a dual catalytic system for the activation of alkyne, enabling attack from weak nucleus[2].
Fig.2 The activation of C-C triple bond catalyzed by eosin Y and Cu(OTF)2 [2]
- Photocatalytic three-component reductive coupling reactions
Chiral α-branched amines and their derivatives are common in pharmaceuticals, agrochemicals and biologically relevant natural products. Therefore, it is very important to develop new synthetic approaches for this type of compounds. Under the irradiation of green LED light, a (hetero)aromatic amine, a (hetero)aromatic aldehyde and an electron-deficient olefin undergo a three-component reductive coupling reaction in the presence of eosin Y as photocatalyst and Hantzsch ester as the terminal reducing agent, generating γ-amino acid derivatives. Among them, reactive nucleophilic α-amino radical species with high nucleophilicity are generated, which are capable of carbon-carbon bond formation. The reaction is efficient, simple and broad in scope, providing a complementary strategy to existing synthetic methods[3].
Fig.3 The three-component reductive coupling reaction catalyzed by eosin Y[3]
Why choose Alfa Chemistry?
Alfa Chemistry has been specializing in the field of photochemistry for many years. As a supplier of photocatalysts, we offer not only a wide range of known photocatalysts such as acridine, carbazole, ruthenium and iridium photocatalysts, but also other types of photocatalysts such as fluorescein derivative esoin Y, which is most widely applied to photoredox reactions.
What's more, Alfa Chemistry has a professional team, high quality products, competitive prices and the most attentive service. We also offer product customization according to customer's detailed requirements. Please contact us, if you are in need of assistance.
References
- Majek, M.; Filace, F.; von Wangelin, A. Jacobi. On the mechanism of photocatalytic reactions with eosin Y. J. Org. Chem. 2014, 10: 981–989.
- Jin, R. W.; et al. Merging photoredox catalysis with Lewis acid catalysis: activation of carbon-carbon triple bond. Chem. Commun. 2016, 52: 9909-9912
- de Arriba, A. L. F., Urbitsch, F.; Dixon, D. J. Umpolung synthesis of branched α-functionalized amines from imines via photocatalytic three-component reductive coupling reactions. Chem. Commun. 2016, 52: 14434-14437
