Photocatalytic synthesis of anilides from nitrobenzenes under visible light irradiation: 2 in 1 reaction

Accessible, Direct Photochemical Route for the Amine-Free Synthesis of Azoxybenzene and Functional Azoxy Derivatives via Nitroarene Homocoupling

“…11 It has long been known that nitroaromatics can undergo photoreduction upon direct absorption of light. 11,13 Adsorbed nitrobenzene exhibits several attractive electrochemical characteristics. 12 Specifically, there is evidence that this activity is triggered by near UV light through the development of an electrophilic n𝜋* triplet state (Figure 3).…”

“…More specifically, illumination of the nitroarene under an atmosphere of argon at a wavelength of 400 nm causes Habstraction from propylamine, which ultimately results in the generation of key intermediates (nitrosobenzene and phenylhydroxylamine) via subsequent radical creation and rearrangements. 13 The final step, condensation between the aryl nitroso and the aryl hydroxylamine, is carried out in an atmosphere containing oxygen (Figure 4). Due to the fact that this reaction was performed in water, the lack of a strong hydrogen donor source could lead to slow reaction rates.…”

“…including rigorous temperature control and the use of strong acids or bases. 13 Alternatively, the photoinduced reduction of nitrobenzene employs high-energy photons at atmospheric pressure and room temperature; serving as an advancement to the pursuit of environmentally "benign" or "green" syntheses. 15 Moreover, light-driven reactions provide a low-cost, gentle, and "tunable" method for the synthesis of essential molecules, and one-pot reactions are desirable as they avoid the separation of unstable intermediates and limit waste creation.…”

“…In a solvent such as i-PrOH, the excited nitrobenzene at the triplet state abstracts H from the solvent, ultimately resulting in the synthesis of phenylhydroxylamine after a total of four H-atom abstractions: two from the solvent (i-PrOH), and two from radical intermediaries, in a manner comparable to the mechanisms observed with benzophenone. [10][11][12][13][14] The light-induced formation of phenylhydroxylamine is followed by two simultaneous dark reactions: its oxidation to nitrosobenzene and then its condensation with nitrosobenzene to form azoxybenzene (Figure 13).…”

“…In all cases only the specified product (azoxybenzene) and the starting material (nitroarene) were detected in considerable amounts (> 5%) at the completion of each reaction. Column chromatography was utilized for purification of compounds and all products were characterized using 1 H NMR, 13 C NMR, and GC-MS.…”