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Visible-Light Photocatalytic Synthesis of Amines from Imines via Transfer Hydrogenation Using Quantum Dots as Catalysts

Xi, Zi-Wei, Yang, Lei, Wang, Dan-Yan, Pu, Chao-Dan, Shen, Yong-Miao, Wu, Chuan-De, Peng, Xiao-Gang
Journal of organic chemistry 2018 v.83 no.19 pp. 11886-11895
aldehydes, ambient temperature, amines, catalysts, chemical structure, electron transfer, hydrogen, hydrogenation, imines, organic chemistry, photocatalysis, quantum dots
CdSe/CdS core/shell quantum dots (QDs) can be used as stable and highly active photoredox catalysts for efficient transfer hydrogenation of imines to amines with thiophenol as a hydrogen atom donor. This reaction proceeds via a proton-coupled electron transfer (PCET) from the QDs conduction band to the protonated imine followed by hydrogen atom transfer from the thiophenol to the α-aminoalkyl radical. This precious metal free transformation is easy to scale up and can be carried out by a one-pot protocol directly from aldehyde, amine, and thiophenol. Additional advantageous features of this protocol include a wide substrate scope, high yield of the amine products, extremely low catalyst loading (0.001 mol %), high turnover number (10⁵), and the mild reaction conditions of using visible light or sun light at room temperature in neutral media.