NaI/PPh₃-Mediated Photochemical Reduction and Amination of Nitroarenes

Abstract

A mild transition-metal- and photosensitizer-free photoredox system based on the combination of NaI and PPh3 was found to enable highly selective reduction of nitroarenes. This protocol tolerates a broad range of reducible functional groups such as halogen (Cl, Br, and even I), aldehyde, ketone, carboxyl, and cyano. Moreover, the photoredox catalysis with NaI and stoichiometric PPh3 provides also an alternative entry to Cadogan-type reductive amination when o-nitrobiarenes were used.

A Minireview on the Scope of Cadogan Cyclization Reactions Leading to Diverse Azaheterocycles

“…Moreover, to find the reactivities of this visible‐light‐driven nitroarene reduction mediated by NaI/PPh 3 , the authors performed UV‐vis spectroscopic absorption experiments to describe its photoactivating action models. The results were further supported by the DFT study showed the mechanistic insights in the combination of nitroarenes with NaI and PPh 3 formed electron donor‐acceptor complex, which resulted in the absorption of the photons to empower reductive hydrogenation of nitroarenes [32] . Thus, stoichiometric PPh 3 (2.5 equiv.)…”

“…The results were further supported by the DFT study showed the mechanistic insights in the combination of nitroarenes with NaI and PPh 3 formed electron donor-acceptor complex, which resulted in the absorption of the photons to empower reductive hydrogenation of nitroarenes. [32] Thus, stoichiometric PPh 3 (2.5 equiv.) and the photocatalyst-free NaI (40 mol%)/PPh 3 based photocatalysis can be used as a very effective and efficient method for Cadogan-type reductive amination of onitrobiarenes for the preparation of carbazoles (Scheme 10).…”

“…In the same year, a mild NaI/PPh 3 -mediated photosensitizer-free photochemical selective reduction and amination of nitroarenes was described by Zhonghua Qu and colleagues to synthesize a series of carbazoles 44 as shown in Scheme 10. [32] The salient features of this methodology include sufficient substrate scope including tolerance of a broad range of functional groups comprising halogens, aldehyde, ketone, carboxyl, and cyano under mild reaction conditions and without using transition metal catalysts. Moreover, to find the reactivities of this visible- light-driven nitroarene reduction mediated by NaI/PPh 3 , the authors performed UV-vis spectroscopic absorption experiments to describe its photoactivating action models.…”

“…Compound 40 prepared through Suzuki coupling, was treated with PPh 3 in o ‐DCB, resulting in the formation of a mixture of 41 a – b , which were later hydrolysed to yield corresponding carboxylic acids 42 a – b (Scheme 9). In the same year, a mild NaI/PPh 3 ‐mediated photosensitizer‐free photochemical selective reduction and amination of nitroarenes was described by Zhonghua Qu and colleagues to synthesize a series of carbazoles 44 as shown in Scheme 10 [32] . The salient features of this methodology include sufficient substrate scope including tolerance of a broad range of functional groups comprising halogens, aldehyde, ketone, carboxyl, and cyano under mild reaction conditions and without using transition metal catalysts.…”

Facile synthesis of Pd@MOF catalyst and its application for High Selective Hydrogenation and Hydrodeoxygenation of Biomass-Derived Compounds

“…The catalytic performance of Pd@MOF for the HDO reaction of nitroarenes is perfect, its hydrodeoxygenated products, and aromatic amines have been widely used as chemical intermediates for pharmaceutical synthesis. 34,35 The catalytic activity of Pd@MOF in nitroarenes hydrodeoxygenation was tested (Table 3, entry 6-8). For nitroarenes containing electronwithdrawing group and electron-donating group, such as -CH3 and -F, above 99% conversion of aromatic amines can be obtained within 3 h (entries 6, 7, and 8 Table 3).…”