Visible Light Photocatalytic Radical–Radical Cross-Coupling Reactions of Amines and Carbonyls: A Route to 1,2-Amino Alcohols

Abstract

An intermolecular radical-radical cross-coupling reaction of secondary and tertiary amines with aryl ketones and aldehydes has been developed using visible light photoredox catalysis. This reaction provides an efficient and straightforward approach to some useful 1,2-amino alcohols in moderate to good yields under mild conditions.

N‐Arylamines Coupled with Aldehydes, Ketones, and Imines by Means of Photocatalytic Proton‐Coupled Electron Transfer

“…Previous reports of visible‐light induced ketyl radical formation reactions are enhanced by the addition of acids, which were consistent with this reaction when a catalytic amount of oxalic acid was added (entry 4, 63 % yield). Furthermore, to suppress the possible formation of undesired diol, and coordinate α‐amino radical and ketyl radical cross‐coupling by Li + , we added a lithium salt (LiBF 4 , 1 equiv) to the reaction mixture and found that the yield improved to 72 % (entry 5, 70 % isolated yield). In the absence of DABCO and acid, a sharp decrease in efficiency was found (entry 6), which indicated that the lithium salt serves as a Lewis acid to induce a Lewis acid‐activated single electron transfer (SET) process to afford corresponding ketyl radical is impossible .…”

Recent Advances in Photocatalytic Functionalization of Quinoxalin‐2‐ones

“…In 2016, the researchers from the group of Xiao were able to generate the α-amino radical of 3,4-dihydroquinoxalin-2-one (among other amines) using fac-Ir(ppy) 3 as photocatalyst. [83] They reported just two examples in which this radical was coupled with benzophenone through its lithium-bonded ketyl radical (Scheme 64). These researchers were also capable of proposing a mechanistic pathway by which its developed reaction should proceed.…”

Recent Advances in Rapid Synthesis of Non-proteinogenic Amino Acids from Proteinogenic Amino Acids Derivatives via Direct Photo-Mediated C–H Functionalization

“…While in Wang's work, the authors proposed a proton-coupled electron transfer (PCET) pathway of the complex containing the aldehyde, DABCO, and a protonic acid (Scheme 21). Since 2016, Xiao's group [49] and Wang's group [50] have developed the photocatalytic benzylation of glycine derivatives with ketones and aldehydes, respectively, to produce useful 1,2-amino alcohols in moderate efficiency. Xiao and coworkers believed that the lithium salt LiBF 4 took the important role as a Lewis acid in the activation of the ketones to the corresponding ketyl radical (Scheme 20).…”