Denitrative functionalization of nitroarenes
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REVIEW
Denitrative functionalization of nitroarenes Sajedeh Maddah‑Roodan1,2 · Roghaye Soltani1,3 · Arash Ghaderi1 Received: 22 June 2020 / Accepted: 31 August 2020 © Iranian Chemical Society 2020
Abstract Denitrative functionalization of nitroaromatic compounds has become a very intriguing challenge in synthetic chemistry. Herein, various methodologies for Csp2–NO2 bond cleavage of nitroaromatic compounds have been reviewed. We survey the literature for the reactions in which nitroarenes have been used as the electrophilic coupling partners for the formation of Csp2–O, Csp2–S, Csp2–N, Csp2 –H and Csp2 –C bonds via transition metal-catalyzed cross-coupling reactions. A brief discussion about the mechanism of the reactions has also been presented. Keywords Denitrative functionalization · Nitroarenes · C–N bond cleavage
Introduction Many important compounds used in the chemical industry contain at least one nitrogen atom [1]. One of these compounds is nitroarenes which is used as the feedstocks for pesticides, dyes, explosives and pharmaceuticals [2, 3]. Due to the electron-withdrawing nature of the nitro group and the stability of its bond to aromatic rings and also the prevalence of nitroarenes, these compounds are attractive reagents in organic synthesis [4–11]. Breaking the Csp2–NO2 bond in nitroarenes is a great challenge for researchers because the resonance and electron-withdrawing properties of the nitro group make these compounds highly stable. Traditionally, a three-step process is used to break the Csp2–NO2 bond; (1) reducing the nitro group and converting it to a primary amine, (2) diazotization and (3) displacement by a nucleophile. An alternative process employed to break the Csp2–NO2 bond is through direct nucleophilic aromatic substitution Sajedeh Maddah-Roodan and Roghaye Soltani have contributed equally in this review. * Arash Ghaderi [email protected] 1
Department of Chemistry, College of Sciences, University of Hormozgan, 7916193145 Bandar Abbas, Iran
2
Department of Chemistry, Faculty of Science, University of Yazd, 89195‑741 Yazd, Iran
3
Department of Chemistry, Faculty of Science, Ferdowsi University of Mashhad, 9177948974 Mashhad, Iran
(SNAr). The presence of electron-withdrawing groups in the ortho or para position of nitroarenes makes the Csp2 –NO2 bond more polarized, and this facilitates breaking the Csp2–NO2 bond through S NAr reactions. Due to the increased polarity of Csp2–NO2 bond in nitroarenes, the rate and efficiency of these SNAr reactions are improved in polar aprotic solvents. As an example, the activity of the leaving groups in the phenoxides substitution reactions with nitro and halo-phthalimides in the DMF and DMSO solvents was studied, and the order of reactivity in these reactions was NO2 > F > C1 (Scheme 1) [12]. The nature of the nucleophile in the SNAr reaction has an important effect on the reaction [13]. For example, anhydrous TBAF was used as a source of fluoride ion in the fluorodenitration reaction (Scheme 2). Due to the high electron
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