Study On Amination Of Benzo - Oxazole Derivatives By Visible Light Photocatalyst

2-Aminobenzoxazoles play an important role in biological, pharmaceutical, and material science, the development of synthetic strategies for their synthesis is an important issue. In recent years, direct C-H functionalization is a desirable transformation in organic synthesis, as it does not require prefunctionalization of the substrates to be modified, thus providing atom economy, rapid and environmentally benign protocols for the construction of new chemical bonds. The direct amination of benzoxazoles is an ideal protocol for the synthesis of2-aminobenzoxazoles including copper-catalyzed or copper-mediated amination and acid-promoted amination. Chemists still try to expand the method for the synthesis of these kinds of compounds.Visible light photoredox catalysis has received much attention recently toward the organic synthesis. Many of the most commonly employed visible light photocatalysts are organic dyes and polypyridyl complexes of ruthenium and iridium. These complexes absorb the visible light giving photoexcited states that are very potent single-electron-transfer reagents which induce unique and valuable catalytic processes. It has been employed to perform a cycloaddition, an arylation of heterocycles, dehalogenation of activated alkyl halides and many other reactions. Photoredox reactions which are employed to generate radicals occur under extremely mild conditions, with most reactions proceeding at room temperature without the need for highly reactive radical initiators or the specialized irradiation equipment compared to the normal photochemistry. Besides, photoredox catalysts may be employed at very low loadings and has been merged with transition metal catalysis to achieve varies bond constructions. Despite these advances, the direct amination of benzoxazoles under visible light photoredox catalysis is still a challenge for chemists.Herein we report a "radical-type" amination of benzoxazoles with chloroamines prepared in situ promoted by visible light, which provides a general and valuable method for the synthesis of2-aminobenzoxazoles. Investigations focused on the time, the temperature, the atmosphere, the catalysts, the additives and the solvents to give the best yield. Under the optimized reaction conditions, we next investigated the substrate scope of the reaction. We varied the benzoxazole core with the cyclic and non-cyclic secondary aliphatic amines which all provided the desired products in good yields. We then developed a convenient direct amination sequence that is one-pot two-steps methods. Besides, we investigate the reaction mechanism which is not very clear at this moment. This novel method was also applied to the synthesis of a coumarin derivative which displays potent anti-HIV and antitumor activities.