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pH-Regulated transfer hydrogenation of quinoxalines with a Cp*Ir–diamine catalyst in aqueous media
- Tan, Jing, Tang, Weijun, Sun, Yawei, Jiang, Zhen, Chen, Fei, Xu, Lijin, Fan, Qinghua, Xiao, Jianliang
- Tetrahedron 2011 v.67 no.34 pp. 6206-6213
- catalysts, chemical structure, hydrogen, hydrogenation, nitrogen, pH, quinoxalines
- The combination of [Cp*IrCl₂]₂ with N-(2-aminoethyl)-4-(trifluoromethyl)benzenesulfonamide constitutes an efficient catalyst for selective transfer hydrogenation of a variety of quinoxalines in water with HCOONa as the hydrogen source, affording the corresponding tetrahydroquinoxalines in good to excellent yields. The catalyst is air-stable, and the reduction could be performed without nitrogen protection. The aqueous phase reduction is shown to be highly pH-dependent, with acidic pH leading to better results. There exits a pH window for optimum rate, and the use of HOAc/NaOAc buffer solution is essential for maintaining a stable pH during the reaction.