- Metal-free oxidative decarbonylative halogenation of fused imidazoles
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An efficient strategy has been developed for the deformylative halogenation of carbaldehyde imidazo-fused heterocycles in the presence of TBHP controlled by temperature. A convenient and sequential functionalization (C8 to C3) portrays the synthetic utility of the current method.N-Heterocycle benzamide products were also observedviathe ring opening of imidazopyridines through the cleavage of C-C bond at high temperatures. Features of this method include temperature-controlled excellent regioselectivity, mild conditions and functional group tolerance.
- Kumar, Gulshan,Shankar, Ravi,Singh, Davinder,Tali, Javeed Ahmad
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p. 20551 - 20555
(2021/11/23)
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- Sustainable photocatalytic synthesis of benzimidazoles
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Among the 17 Sustainable Development Goals presented by the United Nations in 2015, great attention is devoted to the production of goods and chemicals by use of renewable raw materials, by recycling of products and by extensive use of renewable energy sources. In this context, photocatalysis attracted great attention for the possibility to exploit Solar light to promote the desired chemical reactions. Besides its use in degradation of pollutants and in the production of fuels, some efforts have been devoted in the development of photocatalytic processes for the synthesis of fine chemicals with high added-value. In this work, we investigated the sustainable photocatalytic synthesis of benzimidazole derivatives through a one-pot, tandem process starting from a nitro compound and ethanol. By a photocatalytic approach, ethanol is dehydrogenated producing the hydrogen required for reduction of nitro groups and the aldehyde required for cyclization and production of the benzimidazole unit. Co-doping of TiO2 with B and N is beneficial to increase the photocatalytic activity in H2 production from ethanol. The effect of various metal co-catalysts (Pt, Pd Ag, Cu) have been evaluated on H2 production rate and on selectivity in the synthesis of substituted benzimidazoles: Pt showed the highest selectivity in the desired products while Pd demonstrated a great activity for hydrodehalogenation, with potential interest for degradation of persistent pollutants.
- Montini, Tiziano,Gombac, Valentina,Delgado, Juan J.,Venezia, Anna Maria,Adami, Gianpiero,Fornasiero, Paolo
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- 1,2-Disubstituted Benzimidazoles by the Iron Catalyzed Cross-Dehydrogenative Coupling of Isomeric o-Phenylenediamine Substrates
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Benzimidazoles are common in nature, medicines, and materials. Numerous strategies for preparing 2-arylbenzimidazoles exist. In this work, 1,2-disubstituted benzimidazoles were prepared from various mono- and disubstituted ortho-phenylenediamines (OPD) by iron-catalyzed oxidative coupling. Specifically, O2 and FeCl3·6H2O catalyzed the cross-dehydrogenative coupling and aromatization of diarylmethyl and dialkyl benzimidazole precursors. N,N′-Disubstituted-OPD substrates were significantly more reactive than their N,N-disubstituted isomers, which appears to be relative to their propensity for complexation and charge transfer with Fe3+. The reaction also converted N-monosubstituted OPD substrates to 2-substituted benzimidazoles; however, electron-poor substrates produce 1,2-disubstituted benzimidazoles by intermolecular imino-transfer. Kinetic, reagent, and spectroscopic (UV-vis and EPR) studies suggest a mechanism involving metal-substrate complexation, charge transfer, and aerobic turnover, involving high-valent Fe(IV) intermediates. Overall, comparative strategies for the relatively sustainable and efficient synthesis of 1,2-disubstituted benzimidazoles are demonstrated.
- Foss, Frank W.,Palacios, Philip M.,Pierce, Brad S.,Thapa, Pawan,Tran, Tam
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p. 1991 - 2009
(2020/03/13)
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- Green synthesis of privileged benzimidazole scaffolds using active deep eutectic solvent
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The exploitation and use of alternative synthetic methods, in the face of classical procedures that do not conform to the ethics of green chemistry, represent an ever-present problem in the pharmaceutical industry. The procedures for the synthesis of benzimidazoles have become a focus in synthetic organic chemistry, as they are building blocks of strong interest for the development of compounds with pharmacological activity. Various benzimidazole derivatives exhibit important activities such as antimicrobial, antiviral, anti-inflammatory, and analgesic activities, and some of the already synthesized compounds have found very strong applications in medicine praxis. Here we report a selective and sustainable method for the synthesis of 1,2-disubstituted or 2-substituted benzimidazoles, starting from o-phenylenediamine in the presence of different aldehydes. The use of deep eutectic solvent (DES), both as reaction medium and reagent without any external solvent, provides advantages in terms of yields as well as in the work up procedure of the reaction.
- Gioia, Maria Luisa Di,Cassano, Roberta,Costanzo, Paola,Cano, Natividad Herrera,Maiuolo, Loredana,Nardi, Monica,Nicoletta, Fiore Pasquale,Oliverio, Manuela,Procopio, Antonio
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supporting information
(2019/08/20)
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- Selective and eco-friendly procedures for the synthesis of benzimidazole derivatives. The role of the Er(OTf)3 catalyst in the reaction selectivity
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An improved and greener protocol for the synthesis of benzimidazole derivatives, starting from o-phenylenediamine, with different aldehydes is reported. Double-condensation products were selectively obtained when Er(OTf)3 was used as the catalyst in the presence of electron-rich aldehydes. Conversely, the formation of mono-condensation products was the preferred path in absence of this catalyst. One of the major advantages of these reactions was the formation of a single product, avoiding extensive isolation and purification of products, which is frequently associated with these reactions. Theoretical calculations helped to understand the different reactivity established for these reactions. Thus, we found that the charge density on the oxygen of the carbonyl group has a significant impact on the reaction pathway. For instance, electron-rich aldehydes better coordinate to the catalyst, which favours the addition of the amine group to the carbonyl group, therefore facilitating the formation of double-condensation products. Reactions with aliphatic or aromatic aldehydes were possible, without using organic solvents and in a one-pot procedure with short reaction time (2-5 min), affording single products in excellent yields (75-99%). This convenient and eco-friendly methodology offers numerous benefits with respect to other protocols reported for similar compounds.
- Herrera Cano, Natividad,Uranga, Jorge G.,Nardi, Mónica,Procopio, Antonio,Wunderlin, Daniel A.,Santiago, Ana N.
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supporting information
p. 2410 - 2419
(2016/12/07)
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- Supercritical methanol as solvent and carbon source in the catalytic conversion of 1,2-diaminobenzenes and 2-nitroanilines to benzimidazoles
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Benzimidazoles and N-methylbenzimidazoles were synthesized by simply heating 1,2-diaminobenzenes in supercritical methanol over copper-doped porous metal oxides. These catalysts were derived from synthetic hydrotalcites that only contain earth-abundant starting materials. The carbon equivalents needed for the construction of the benzimidazole core originated from the solvent itself, which is known to undergo reforming to hydrogen and carbon monoxide through the formation of a formaldehyde intermediate. A variety of 1,2-diaminobenzenes were converted to the corresponding mixtures of benzimidazoles and N-methylated analogues in good yields. Interestingly, the more challenging, but readily available 2-nitroanilines, which require an additional reduction step prior to cyclization, could also be successfully converted to benzimidazoles in high selectivity. Furthermore, various other alcohols were applied besides methanol, to obtain 2-alkyl- and 1,2-dialkylbenzimidazoles. Preliminary mechanistic insights into the origins of N-alkylation as well as the reactivity of the nitro derivatives are discussed.
- Sun, Zhuohua,Bottari, Giovanni,Barta, Katalin
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p. 5172 - 5181
(2015/12/08)
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- Synthesis of benzimidazoles via iridium-catalyzed acceptorless dehydrogenative coupling
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Iridium-catalyzed acceptorless dehydrogenative coupling of tertiary amines and arylamines has been developed. A number of benzimidazoles were prepared in good yields. An iridium-mediated C-H activation mechanism is suggested. This finding represents a novel strategy for the synthesis of benzimidazoles.
- Sun, Xiang,Lv, Xiao-Hui,Ye, Lin-Miao,Hu, Yu,Chen, Yan-Yan,Zhang, Xue-Jing,Yan, Ming
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p. 7381 - 7383
(2015/07/15)
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- Synthesis of benzimidazoles via iridium-catalyzed acceptorless dehydrogenative coupling
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Iridium-catalyzed acceptorless dehydrogenative coupling of tertiary amines and arylamines has been developed. A number of benzimidazoles were prepared in good yields. An iridium-mediated C-H activation mechanism is suggested. This finding represents a novel strategy for the synthesis of benzimidazoles.
- Sun, Xiang,Lv, Xiao-Hui,Ye, Lin-Miao,Hu, Yu,Chen, Yan-Yan,Zhang, Xue-Jing,Yan, Ming
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p. 7381 - 7383
(2015/11/27)
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- Green syntheses of n-alkyl-2-styrylbenzimidazoles
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Simple and green methodologies for the syntheses of 2-styrylbenzimidazoles (3a-c) and its N-alkyl derivatives (7a-i) have been developed. o-Phenylenediamine (1) was condensed with cinnamic acids (2a-c) resulting in 2-styrylbenzimidazoles (3a-c) using glycerol as a green and efficient solvent. 3 were also prepared alternatively by the condensation of 2-methylbenzimidazole (4) with benzaldehydes (5a-c) using glycerol as solvent. 2-Styrylbenzimidazoles (3a-c) and 2-methylbenzimidazole (4) were alkylated independently to obtain N-alkyl- 2-styrylbenzimidazole (7a-i) and N-alkyl-2-methylbenzimidazole (6a-c), respectively using DMS/DES/PhCH2Cl applying green methods such as simple physical grinding of reactants in solid phase, treating reactants in PEG-600 as a solvent in solution phase and using microwave irradiation of reactants respectively. Compounds 7a-i could also be prepared, alternatively, by heating 6a-c with 5a-c in glycerol at 180 °C for 3-4 h.
- Kumar, T. Ashok,Devi, B. Rama,Dubey
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p. 9569 - 9572
(2014/01/06)
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- Synthesis of annulated benzimidazoles via amidine cyclization
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Structurally diverse annulated benzimidazoles were synthesized via two copper(I)-catalyzed cyclocondensation reactions. In the first case the title compounds were prepared from lactams and o-bromoaniline. An alternative route consisted of an intramolecular cyclization of o-bromoarylamidines.
- Liubchak, Kostiantyn,Nazarenko, Kostiantyn,Tolmachev, Andrey
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experimental part
p. 2993 - 3000
(2012/05/31)
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- A combined-redox synthesis of 2-alkylbenzimidazoles from 2-nitroanilines by semiconductor photocatalysis
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One-pot photocatalytic synthesis of 2-substituted benzimidazoles from 2-nitroanilines with different alcohols by combined redox cyclization reaction using TiO2-P25 is reported. The reaction, when performed with ethanol, gives 2-methylbenzimidazole as a single product. However, in a mixture of ethanol and water (1:1), it gives both 2-methylbenzimidazole and 1-ethyl-2-methylbenzimidazole. The products have been characterized by Fourier transorm-infrared, 1H NMR, 13CNMR, and gas chromatography-mass spectrometry analysis. TiO2-P25 behaves as a combined redox photocatalyst by reducing 2-nitroaniline and oxidizing alcohols simultaneously under ultraviolet light. Easy product isolation under mild conditions and good yield make this one-pot synthesis ecofriendly. Copyright Taylor & Francis Group, LLC.
- Annadhasan,Selvam,Swaminathan
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scheme or table
p. 1500 - 1508
(2012/04/17)
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- Ultrasound promoted simple and efficient N-alkylation of 2-substituted benzimidazoles
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N-Alkylation of 2-chlorobenzimidazole was carried out using different alkylating agents under ultrasound irradiation technique. These reactions were completed in shorter times and with higher percentage of yields. Among all the green solvents, triethanolamine was found to be very effective and also acts as a base. The above reaction conditions were extended to other 2-substituted benzimidazoles. Thus, a simple and efficient route for N-alkylation has been developed using ultrasound irradiation technique.
- Babu, P. N. Kishore,Devi, B. Rama,Dubey, P. K.
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p. 5756 - 5758,3
(2020/09/14)
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- Synthesis of benzimidazoles by phosphine-mediated reductive cyclisation of ortho-nitro-anilides
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Heating ortho-nitro-anilides 1-3 and 2-methyl-N-(3-nitropyridin-2-yl) propanamide (5) with 4 equiv. of a phosphine led to the 2-substituted benzimidazoles 6-8 and to the imidazo[4,5-b]pyridine 10, respectively, in yields between 45 and 85%. Heating 1 with (EtO)3P effected cyclisation and N-ethylation, leading to the 1-ethylbenzimidazole 6b. The slow cyclisation of the N-pivaloylnitroaniline 2b allowed isolation of the intermediate phosphine imide 11 that slowly transformed into the 1H-benzimidazole 7b. The structure of 11 was established by crystal-structure analysis. While the N-methylated ortho-nitroacetanilide 3 cyclised to the 1,2-dimethyl-1H-benzimidazole (8), the 2-methylpropananilide 4 was transformed into 1-methyl-3-(1-methylethyl)-2H- benzimidazol-2-one (9).
- Duchek, Jan,Vasella, Andrea
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experimental part
p. 977 - 986
(2011/08/05)
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- An easy one-step photocatalytic synthesis of 1-aryl-2-alkylbenzimidazoles by platinum loaded TiO2 nanoparticles under UV and solar light
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One-pot synthesis of disubstituted benzimidazoles from N-substituted 2-nitroanilines or 1,2-diamines with 3-12 nm-sized platinum particles loaded on the TiO2 using solar and UV-A light is described. 1-Aryl-2-alkylbenzimidazoles from 2-nitrodiphenylamines are formed by combined redox photocatalytic reaction, condensation and catalytic dehydrogenation on Pt-TiO2. In case of diamines, this reaction is proceeded by Pt-TiO2 assisted photocatalytic oxidation of an alcohol and a catalytic dehydrogenation of the intermediate on the surface of platinum nanoparticles. In both cases product formation was achieved by tandem photocatalytic and catalytic reactions on Pt-TiO2.
- Selvam,Swaminathan
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experimental part
p. 3386 - 3392
(2011/06/28)
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- Synthesis of 2-arylbenzothiazoles and imidazoles using scandium triflate as a catalyst for both a ring closing and an oxidation steps
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2-Aminobenzenethiol and an aryl aldehyde were allowed to react to give a 2-arylbenzothiazole in good yield in the presence of a catalytic amount of scandium triflate Sc(OTf)3. The detailed study showed that Sc(OTf)3 catalyzed two steps, that is, the formation of a thiazoline ring and the oxidation of the thiazoline to a thiazole ring. This is the first example that scandium(III) ion catalyzed oxidation of an organic compound using molecular oxygen as an oxidant. The reaction was applied to o-phenylenediamine and an aryl aldehyde to give corresponding 2-arylbenzimidazole in moderate to good yields depending upon the structure of aldehyde.
- Itoh, Takashi,Nagata, Kazuhiro,Ishikawa, Hiroyuki,Ohsawa, Akio
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p. 2769 - 2783
(2007/10/03)
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- Synthesis of 2-substituted benzimidazoles by reaction of o-phenylenediamine with aldehydes in the presence of Sc(OTf)3
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2-Substituted benzimidazoles were synthesised under mild conditions by reaction of o-phenylenediamine with aldehydes in the presence of Sc(OTf) 3 as a Lewis acid catalyst.
- Nagata, Kazuhiro,Itoh, Takashi,Ishikawa, Hiroyuki,Ohsawa, Akio
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- An intramolecular palladium-catalysed aryl amination reaction to produce benzimidazoles
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A novel synthesis of benzimidazoles by a palladium-catalysed intramolecular N-arylation reaction from (o-bromophenyl)amidine precursors is described.
- Brain, Christopher T,Brunton, Shirley A
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p. 1893 - 1895
(2007/10/03)
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