Thiobenzoic Acid-Catalyzed Regioselective Functionalization of Allylamines via Hydrogen Atom Transfer under Visible Light Irradiation

Abstract

Since allylamines are easily accessible and can serve as key intermediates in the synthesis of bioactive compounds, selective transformations are extremely useful. So far, however, reactions of allylamines via hydrogen atom abstraction under photoirradiation have been little studied. Herein, we report regioselective C-H functionalization of allylamines catalyzed by thiobenzoic acid (TBA) as a dual-role (SET/HAT) photocatalyst under visible light irradiation (455 nm). In the coupling of N,Ndialkyl allylamines with cyanoarenes, γ-arylated α-aminonitriles were obtained in a highly regioselective manner. In contrast, γ-arylated enamines were obtained when N,N-diaryl allylamines were used as C-H donor substrates. In reactions with electron-accepting reagents that are less reducible than 1,4-dicyanobenzene, such as cyanopyridines and arylketones, protic solvents and B(OMe)3 were effective for activation, affording the corresponding γ-pyridinylated and hydroxyalkylated products in good to high yield. By appropriately varying the substrates and the reaction conditions, four types of medicinally attractive amine-containing compounds were synthesized. Considering the inherent redox reactivity of the allylamine substrates as well as the enamine intermediates, the mild photocatalytic activity of TBA is likely to be the key to achieving selective C-H transformation of allylamines.