Pd-catalyzed dehydrogenative arylation of arylhydrazines to access non-symmetric azobenzenes, including tetra-ortho derivatives

• Loris Geminiani,
• Kathrin Junge,
• Matthias Beller and
• Jean-François Soulé

Beilstein J. Org. Chem. 2025, 21, 2234–2242, doi:10.3762/bjoc.21.170

• , most synthetic methods have focused on the preparation of symmetric derivatives [12][13]. Traditional approaches, such as oxidative coupling of anilines [14][15][16][17][18][19], reductive coupling of nitroarenes [20][21][22][23], or cross-coupling between anilines and nitroarenes have proven

C2 to C6 biobased carbonyl platforms for fine chemistry

• Jingjing Jiang,
• Muhammad Noman Haider Tariq,
• Florence Popowycz,
• Yanlong Gu and
• Yves Queneau

Beilstein J. Org. Chem. 2025, 21, 2103–2172, doi:10.3762/bjoc.21.165

Facile one-pot reduction of β-nitrostyrenes to phenethylamines using sodium borohydride and copper(II) chloride

• Laura D’Andrea and
• Simon Jademyr

Beilstein J. Org. Chem. 2025, 21, 39–46, doi:10.3762/bjoc.21.4

• limited, since a NaBH4/transition metal salt system is mostly used to reduce nitroarenes [23][24][25][26]. One of the reported methods takes advantage of titanium(IV) isopropoxide as a catalyst to prepare varied β-phenethylamine analogues. Despite its simplicity, the reaction time is quite prolonged (from

Electrocatalytic hydrogenation of cyanoarenes, nitroarenes, quinolines, and pyridines under mild conditions with a proton-exchange membrane reactor

• Koichi Mitsudo,
• Atsushi Osaki,
• Haruka Inoue,
• Eisuke Sato,
• Naoki Shida,
• Mahito Atobe and
• Seiji Suga

Beilstein J. Org. Chem. 2024, 20, 1560–1571, doi:10.3762/bjoc.20.139

• cyanoarenes, nitroarenes, quinolines, and pyridines using a proton-exchange membrane (PEM) reactor was developed. Cyanoarenes were then reduced to the corresponding benzylamines at room temperature in the presence of ethyl phosphate. The reduction of nitroarenes proceeded at room temperature, and a variety of

• cyanoarenes is a straightforward and powerful method for the synthesis of primary amines [5], and the reduction of nitroarenes is useful for the synthesis of aniline derivatives [6][7][8][9][10][11]. Nitrogen-containing aliphatic heterocycles, such as piperidines and tetrahydroquinolines, are key motifs in

• , and pyridines using PEM reactors [51][52]. In this context, we have focused on the synthesis of nitrogen-containing molecules using a PEM reactor. Herein, we report the application of a PEM reactor for the reduction of cyanoarenes, nitroarenes, quinolines, and pyridines. These reductions proceeded

Manganese-catalyzed C–C and C–N bond formation with alcohols via borrowing hydrogen or hydrogen auto-transfer

• Mohd Farhan Ansari,
• Atul Kumar Maurya,
• Abhishek Kumar and
• Saravanakumar Elangovan

Beilstein J. Org. Chem. 2024, 20, 1111–1166, doi:10.3762/bjoc.20.98

• regeneration of complex Mn7-a (Scheme 14). In 2020, Morrill's group reported the one-pot synthesis of N-methylarylamines from nitroarenes using methanol as a methylating agent and reductant [44]. When substituted nitroarenes were methylated with methanol under optimal conditions (5 mol % Mn3, 2 equiv of KOH at

• 110 °C for 16 h), moderate to good yields of N-methylamines were produced (Scheme 15). The mechanistic studies suggested that the base activates the complex Mn3. The active catalyst dehydrogenates methanol into formaldehyde and converts nitroarenes to anilines via transfer hydrogenation. The latter

Carbonylative synthesis and functionalization of indoles

• Alex De Salvo,
• Raffaella Mancuso and
• Xiao-Feng Wu

Beilstein J. Org. Chem. 2024, 20, 973–1000, doi:10.3762/bjoc.20.87

• -arylindoles by reductive carbonylation of unfunctionalized nitroarenes in the presence of arylalkynes and Pd(phen)2(BF4)2 as catalyst has been demonstrated by Cenini's group. The reaction was regioselective, with no detection of 2-arylindole byproducts. No prefunctionalization of the ortho position of the

• aminocarbonylation with nitroarenes as nitrogen source [78]. In this case just one example of indole functionalization was reported. In 2019, Zhao and co-workers, reported an interesting method to synthesize indole-2-carboxylates through a Rh-catalyzed direct C–H alkoxycarbonylation of indoles [79]. The reaction

Recent advancements in iodide/phosphine-mediated photoredox radical reactions

• Tinglan Liu,
• Yu Zhou,
• Junhong Tang and
• Chengming Wang

Beilstein J. Org. Chem. 2023, 19, 1785–1803, doi:10.3762/bjoc.19.131

• academic research and industrial applications. As a result, significant efforts have been devoted to the development of various methods for the reduction of nitroarenes [39]. Recent advancements in the catalytic reduction of nitroarenes largely rely on transition-metal catalysis through direct

• nitroarenes 48 (Scheme 22). The protocol demonstrated excellent tolerance towards a wide range of reducible functional groups, including halogens (such as chlorine, bromine, and even iodine), aldehydes, ketones, carboxyl groups, and cyano groups. Iodination Alkyl iodide is considered to be the most reactive

• photocatalytic decarboxylative radical cascade alkylarylation. Proposed mechanism of the NaI/PPh3-driven photocatalytic decarboxylative radical cascade cyclization. Visible-light-promoted decarboxylative cyclization of vinylcycloalkanes. NaI/PPh3-mediated photochemical reduction and amination of nitroarenes

Clauson–Kaas pyrrole synthesis using diverse catalysts: a transition from conventional to greener approach

• Dileep Kumar Singh and
• Rajesh Kumar

Beilstein J. Org. Chem. 2023, 19, 928–955, doi:10.3762/bjoc.19.71

• aromatization steps led to product 43 upon catalyst regeneration. Recently, Ryabchuk et al. [74] used the 3d-metal cobalt catalyst Co/NGr-C@SiO2-L under solvent-free conditions to synthesize various N-aryl-substituted pyrroles 45 in 50–88% yields from the corresponding nitroarenes 44 via the Clauson–Kaas

• reaction involving benign reducing agents H2 or HCOOH or CO/H2O mixtures (Scheme 21). The main advantage of this heterogeneous Co catalyst is that it can be used up to 10 times without significant loss of activity and the active cobalt hydride species selectively reduces nitroarenes to their corresponding

Mild and selective reduction of aldehydes utilising sodium dithionite under flow conditions

• Nicole C. Neyt and
• Darren L. Riley

Beilstein J. Org. Chem. 2018, 14, 1529–1536, doi:10.3762/bjoc.14.129

• piperidines [17], benzil groups [19], nitroarenes and nitroalkanes in the presence of dialkyl viologen electron transfer catalysts [20][21] and immobilized nitroarene’s under phase transfer conditions [22][23]. In this publication we report the efficient reduction of aldehydes under flow conditions utilising

Transition-metal-free [3 + 3] annulation of indol-2-ylmethyl carbanions to nitroarenes. A novel synthesis of indolo[3,2-b]quinolines (quindolines)

• Michał Nowacki and
• Krzysztof Wojciechowski

Beilstein J. Org. Chem. 2018, 14, 194–202, doi:10.3762/bjoc.14.14

• Michal Nowacki Krzysztof Wojciechowski Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland 10.3762/bjoc.14.14 Abstract Indol-2-ylmethyl carbanions stabilized by alkoxycarbonyl, cyano or benzenesulfonyl groups react with nitroarenes to form σH-adducts

• , which in the presence of base (triethylamine or DBU) and trimethylchlorosilane transform into indolo[3,2-b]quinoline derivatives in moderate to good yields. Keywords: carbanions; cyclization; heterocycles; nitroarenes; nucleophilic substitution; silylation; Introduction The indolo[3,2-b]quinoline

• pharmaceutical applications [19]. During our studies on the reactions of nitroarenes with nucleophiles [20][21][22][23], particularly carbanions, we were interested in a direct transformation of the formed σH-adducts into heterocyclic systems – indoles [21][23] and quinolines [21][22]. Quinolines were formed

Nitration of 5,11-dihydroindolo[3,2-b]carbazoles and synthetic applications of their nitro-substituted derivatives

• Roman A. Irgashev,
• Nikita A. Kazin,
• Gennady L. Rusinov and
• Valery N. Charushin

Beilstein J. Org. Chem. 2017, 13, 1396–1406, doi:10.3762/bjoc.13.136

• anthraquinones. Anyway, the discussed transformation is the case of unusual reduction of nitroaromatic compounds. In general, the chemical reactions, leading to direct displacement of the nitro group in nitroarenes with a hydrogen atom, are rare phenomena. For instance, we can mention the reaction of

Continuous-flow synthesis of primary amines: Metal-free reduction of aliphatic and aromatic nitro derivatives with trichlorosilane

• Riccardo Porta,
• Alessandra Puglisi,
• Giacomo Colombo,
• Sergio Rossi and
• Maurizio Benaglia

Beilstein J. Org. Chem. 2016, 12, 2614–2619, doi:10.3762/bjoc.12.257

• conditions, but the presence of noble metal catalysts, packed into disposable cartridges, suffers from functional group compatibility and catalyst poisoning during time. In 2012 Kappe’s research group reported the microwave-assisted continuous-flow synthesis of anilines from nitroarenes using hydrazine as

• . Using both 0.5 mL and 5 mL reactors, under the best reaction conditions, the continuous-flow reduction of different nitroarenes was studied (Scheme 2). As already demonstrated for the batch procedure [8], the reaction in continuo tolerates a large variety of functional groups: aromatic nitro groups are

An efficient synthesis of N-substituted 3-nitrothiophen-2-amines

• Sundaravel Vivek Kumar,
• Shanmugam Muthusubramanian,
• J. Carlos Menéndez and
• Subbu Perumal

Beilstein J. Org. Chem. 2015, 11, 1707–1712, doi:10.3762/bjoc.11.185

• transformation generates two C–C bonds in a single operation and presumably proceeds through a reaction sequence comprising 2-mercaptoacetaldehyde generation, nucleophilic carbonyl addition, annelation and elimination steps. Keywords: C–C bond generation; nitroarenes; nitroketene acetals; sulfur heterocycles

Continuous flow nitration in miniaturized devices

• Amol A. Kulkarni

Beilstein J. Org. Chem. 2014, 10, 405–424, doi:10.3762/bjoc.10.38

• the dehydrating agent [17]. Theoretically, the application of undiluted nitric acid – usually used in excess – is expected to avoid the use of water. In practice, however, the separation of nitroarenes is facilitated in the diluted nitric acid. Nitration with diluted nitric acid generates the

• of different nitroarenes (e.g. nitroglycerin, ethylene glycol dinitrate, diethylene glycol dinitrate, cyclotrimethylenetrinitramine, pentaerythritol tetranitrate, nitrocellulose, etc.). Continuous processes were enforced as they allowed to retain the same scale of operation while keeping the plant

Synthesis of SF₅-containing benzisoxazoles, quinolines, and quinazolines by the Davis reaction of nitro-(pentafluorosulfanyl)benzenes

• Petr Beier and
• Tereza Pastýříková

Beilstein J. Org. Chem. 2013, 9, 411–416, doi:10.3762/bjoc.9.43

• of nitroarenes with nucleophiles have been the focus of many investigations and represent processes that provide a range of useful products. These reactions can proceed in several ways: (a) ipso substitution of the nitro group of nitroarenes; (b) substitution of a halogen in halogen-substituted

• nitroarenes; and (c) substitution of hydrogen in ortho- or para-positions to the nitro group through vicarious or oxidative nucleophilic substitutions. Mechanistic studies have revealed that in all of these reaction pathways, the primary process is the reversible addition of nucleophiles to the ring carbon

Synthesis of diverse indole libraries on polystyrene resin – Scope and limitations of an organometallic reaction on solid supports

• Kerstin Knepper,
• Sylvia Vanderheiden and
• Stefan Bräse

Beilstein J. Org. Chem. 2012, 8, 1191–1199, doi:10.3762/bjoc.8.132

• results in the liquid phase, ortho,ortho-unsubstituted nitroarenes also delivered indole moieties in good yields. Subsequent palladium-catalyzed reactions (Suzuki, Heck, Sonogashira, Stille) delivered, after cleavage, the desired molecules in moderate to good yields over four steps. The scope and

• reactions have been used to create the indole core. Among these, the Bartoli reaction is a straightforward route for the generation of the indole moiety starting from nitroarenes. Some limitations of this useful reaction have been reported, e.g., only ortho-substituted nitroarenes gave good yields of the

• ], palladium-catalyzed indole synthesis [34][35][36][37][38][39][40], cycloaddition strategies [41], C-arylation of substituted acetonitriles or 1,3-dicarbonyl compounds [42], halocyclization [43][44] and finally, reduction of ortho-fluoro-nitroarenes [42]. The significant biological properties and the

Chemoselective reduction of aldehydes by ruthenium trichloride and resin- bound formates

• Basudeb Basu,
• Bablee Mandal,
• Sajal Das,
• Pralay Das and
• Ashis K. Nanda

Beilstein J. Org. Chem. 2008, 4, No. 53, doi:10.3762/bjoc.4.53

• stable and potent hydride source in Pd-catalyzed transfer hydrogenation of functionalized alkenes, imines, nitroarenes and 1,2-diketones [23][24]. Danks et al. also carried out reduction of alkyl cinnamates using polymer supported formate and catalytic RhCl(PPh3)3 (2.5 mol%) under microwave irradiation

• [25]. Pd-catalyzed transfer hydrogenation of nitroarenes using recyclable polymer-supported formate has been investigated by Abiraj et al [26]. Neither of these conditions were, however, effective in reducing aryl ketones. Since aryl alcohols are important compounds, we became interested to look at