We report the selective photoinduced reduction of nitroarenes to N-arylhydroxylamines. The present methodology facilitates this transformation in the absence of catalyst or additives and uses only light and methylhydrazine. This non-catalytic photoinduced transformation proceeds with a broad scope, excellent functional-group tolerance and high yields. The potential of this protocol reflects on the selective and straightforward conversion of two general antibiotic molecules, azomycin and chloramphenicol, to the bio-active hydroxylamine species.

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We report an efficient catalytic protocol that chemoselectively reduces nitroarenes to arylamines, by using methylhydrazine as a reducing agent in combination with the easily synthesized and robust catalyst tris­(N-heterocyclic thioamidate) Co­(III) complex [Co­(κS,N-tfmp2S)3], tfmp2S = 4-(trifluoromethyl)-pyrimidine-2-thiolate. A series of arylamines and heterocyclic amines were formed in excellent yields and chemoselectivity. High conversion yields of nitroarenes into the corresponding amines were observed by using polar protic solvents, such as MeOH and i PrOH. Among several hydrogen donors that were examined, methylhydrazine demonstrated the best performance. Preliminary mechanistic investigations, supported by UV–vis and NMR spectroscopy, cyclic voltammetry, and high-resolution mass spectrometry, suggest a cooperative action of methylhydrazine and [Co­(κS,N-tfmp2S)3] via a coordination activation pathway that leads to the formation of a reduced cobalt species, responsible for the catalytic transformation. In general, the corresponding N-arylhydroxylamines were identified as the sole intermediates. Nevertheless, the corresponding nitrosoarenes can also be formed as intermediates, which, however, are rapidly transformed into the desired arylamines in the presence of methylhydrazine through a noncatalytic path. On the basis of the observed high chemoselectivity and yields, and the fast and clean reaction processes, the present catalytic system [Co­(κS,N-tfmp2S)3]/MeNHNH2 shows promise for the efficient synthesis of aromatic amines that could find various industrial applications.

The synthesis of 3,4-dihydroquinoxalin-2-ones via the selective reduction of aromatic, multifunctional nitro precursors catalyzed by supported gold nanoparticles is reported. The reaction proceeds through the in situ formation of the corresponding amines under heterogeneous transfer hydrogenation of the initial nitro compounds catalyzed by the commercially available Au/TiO2-Et3SiH catalytic system, followed by an intramolecular C-N transamidation upon treatment with silica acting as a mild acid. Under the present conditions, the Au/TiO2-TMDS system was also found to catalyze efficiently the present selective reduction process. Both transfer hydrogenation processes showed very good functional-group tolerance and were successfully applied to access more structurally demanding products bearing other reducible moieties such as chloro, aldehyde or methyl ketone. An easily scalable (up to 1 mmol), low catalyst loading (0.6 mol%) synthetic protocol was realized, providing access to this important scaffold. Under these mild catalytic conditions, the desired products were isolated in good to high yields and with a TON of 130. A library analysis was also performed to demonstrate the usefulness of our synthetic strategy and the physicochemical profile of the derivatives.