关键词: 可见光诱导的协同催化, 环酮肟酯, 氮杂芳基化, 氮杂芳基取代的烷基腈化合物

Nitrogen-containing heterocyclic compounds widely exist in natural products, pharmaceuticals, dyes and materials science. For example, 1,1-diaryl skeleton is an important structural unit in pesticides. The cyano group is a multifunctional group in organic synthesis. So, development of a green and efficient method for the synthesis of alkyl nitriles containing azaaryl structures is of great research significance. Herein, a photoinduced ring-opening/azaarylation of cyclic oxime esters is described. This reaction utilized 2.2 equiv. of diisopropylethylamine (DIPEA) as reductant, 1.5 equiv. of azaaryl nitriles as azaaryl sources, 1 mol% amount of [Ir(dF(CF₃)ppy)₂dtbbpy]PF₆ as photocatalyst, under the blue irradiation for 7 h, and proceeded well via a radical-radical cross coupling mediated by single electron transfer (SET) and energy transfer (EnT) synergistic catalysis. This strategy features well functional group tolerance, broad substrate scope, simple experimental operation, for the facile synthesis of a series of azaaryl substituted aliphatic nitriles in moderate to excellent yields under the mild reaction conditions. At the same time, for the further synthetic application, the gram-scale and sun-irradiated photochemical reaction of model reaction were performed, both obtaining the target product in good yield. In the standard reaction condition, while 1.2 equiv. of DIPEA was used, the target product was obtained in 73% isolated yield. So, in order to gain more insight into this reaction, a series of mechanistic experiments were performed. Meanwhile, radical trapping experiment of 2,2,6,6- tetramethylpiperidin-1-yl)oxyl (TEMPO) displayed the involvement of radical intermediate in model reaction; fluorescence quenching analysis of Ir photocatalyst and some control experiments explained photoinduced single electron reduction of azaaryl nitriles using DIPEA as reductant; UV-vis spectra experiments, photosensitized reaction of cyclic oxime esters, addition of PhSeSePh and 1,1-diaryl ethylene to cyclic oxime esters, confirmed photosensitized pathway of cyclic oxime esters with Ir photocatalyst; the light on/off experiments declared that this reaction is a photoinduced synthetic reaction. And then a plausible mechanism of photoinduced synergistic catalysis is proposed.

Key words: photoinduced synergistic catalysis, cyclic oxime esters, azaarylation, azaaryl substituted aliphatic nitriles