Selectivity control during the solid supported protic acids catalysed synthesis of 1,2-disubstituted benzimidazoles and mechanistic insight to rationalize selectivity

Kumar, Dinesh; Kommi, Damodara N.; Chebolu, Rajesh; Garg, Sanjeev; Kumar, Raj; Chakraborti, Asit K.

doi:10.1039/c2ra21994h

Cited by 45 publications

(25 citation statements)

References 58 publications

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“…The expected 1,2-disubstituted products were obtained in 90%–98% yields. The reaction, as already reported in the literature, proceeds through a bis-imine formation, a rearrangement, and a 1,3-hydride shift pathway that finally afford the 1,2-disubstituted derivatives [67]. The DES formed by choline chloride and the diamine possibly increases the electrophilic character at aldehyde carbon, which will facilitate the nucleophilic addition of o -phenylenediamine to obtain the benzimidazole derivatives.…”

Section: Resultsmentioning

confidence: 73%

Green Synthesis of Privileged Benzimidazole Scaffolds Using Active Deep Eutectic Solvent

et al. 2019

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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.

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Section: Resultsmentioning

confidence: 73%

Green Synthesis of Privileged Benzimidazole Scaffolds Using Active Deep Eutectic Solvent

et al. 2019

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“…However, the yields were low using aliphatic aldehydes together with SDS as catalyst (Table 1, entry 16) [31]. Conversely, good to moderate yields were observed in reactions between benzaldehyde and o -phenylenediamine catalyzed by lanthanum (LaCl 3 ) [32] , SiO 2 /ZnCl 2 [33], polymeric resin-bound hexafluorophosphate ion (PHP) [15], perchloric acid adsorbed on silica gel (HClO 4 –SiO 2 ) [16], polystyrene sulfonic acid [34], HSO 3 Cl in 2-propanol [35], trimethylsilyl chloride (TMSCl) [36], or Amberlite (IR-120) [37]. It is worth mentioning that these previously reported catalysts required longer reaction times than those used in our current protocol (Table 1, entries 17–24).…”

Section: Resultsmentioning

confidence: 99%

Selective and eco-friendly procedures for the synthesis of benzimidazole derivatives. The role of the Er(OTf)₃ catalyst in the reaction selectivity

Cano¹,

Uranga²,

Nardi³

et al. 2016

Beilstein J. Org. Chem.

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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.

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“…Benzimidazoles and their derivatives are an important heterocyclic compounds which are recently known to exhibit interesting pharmacological properties such as ischemia‐reperfusion injury, hypertension, obesity, and their wide range of biological activities including anti‐ulcer, anti‐hypertensive, anti‐viral, anti‐fungal, anti‐cancer, and anti‐histamine . Generally, a direct one pot condensation–aromatization reaction of o ‐phenylenediamines and aldehydes under oxidative condition is documented for the synthesis of 1,2‐disubstituted benzimidazoles . However, many of these methods have several drawbacks such as expensive reagents, oxidation processes, and prolonged reaction times.…”

Section: Resultsmentioning

confidence: 99%

Green Approach for the Domino Reduction/Reductive Amination of Nitroarenes and Chemoselective Reduction of Aldehydes Using Fe/aq. Citric Acid/Montmorillonite K10

Reddy

Sabitha

2018

ChemistrySelect

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We have developed a new and mild method for the direct onepot reduction/reductive amination of nitroarenes with arylaldehydes using Fe/aq citric acid/montmorillonite K10 catalytic system under ambient conditions. This catalyst has excellent functional group compatibility and the reaction provides rapid access to a diverse range of secondary amines. Under the conditions, aromatic aldehydes are selectively reduced to benzyl alcohols in the presence of ketones. A concise and efficient approach to the synthesis of diverse range of 1,2disubstituted benzimidazoles has also been accomplished for the first time from 1,2-dinitrobenzene and aromatic aldehydes using the above catalytic system. The method involves the domino nitro reduction/cyclization/reduction cascade.

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Selectivity control during the solid supported protic acids catalysed synthesis of 1,2-disubstituted benzimidazoles and mechanistic insight to rationalize selectivity

Cited by 45 publications

References 58 publications

Green Synthesis of Privileged Benzimidazole Scaffolds Using Active Deep Eutectic Solvent

Green Synthesis of Privileged Benzimidazole Scaffolds Using Active Deep Eutectic Solvent

Selective and eco-friendly procedures for the synthesis of benzimidazole derivatives. The role of the Er(OTf)₃ catalyst in the reaction selectivity

Green Approach for the Domino Reduction/Reductive Amination of Nitroarenes and Chemoselective Reduction of Aldehydes Using Fe/aq. Citric Acid/Montmorillonite K10

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Selectivity control during the solid supported protic acids catalysed synthesis of 1,2-disubstituted benzimidazoles and mechanistic insight to rationalize selectivity

Cited by 45 publications

References 58 publications

Green Synthesis of Privileged Benzimidazole Scaffolds Using Active Deep Eutectic Solvent

Green Synthesis of Privileged Benzimidazole Scaffolds Using Active Deep Eutectic Solvent

Selective and eco-friendly procedures for the synthesis of benzimidazole derivatives. The role of the Er(OTf)3 catalyst in the reaction selectivity

Green Approach for the Domino Reduction/Reductive Amination of Nitroarenes and Chemoselective Reduction of Aldehydes Using Fe/aq. Citric Acid/Montmorillonite K10

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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