Iron-Catalyzed Highly Efficient Aerobic Oxidative Synthesis of Benzimidazoles, Benzoxazoles, and Benzothiazoles Directly from Aromatic Primary Amines Under Solvent-Free Conditions in the Open Air

Yu, Jiatao; Xia, Yonggen; Lu, Ming

doi:10.1080/00397911.2014.914221

Cited by 32 publications

(14 citation statements)

References 28 publications

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“…Many synthetic methods describe the oxidative formation of 2-substituted benzothiazoles from 2-aminothiophenol (Scheme 2, compound 1 ) and aldehydes under various aerobic and dehydrogenative conditions [38, 43–45]. Generally, this transformation can be envisioned from the initial, reversible condensation of an aldehyde, e.g.…”

Section: Resultsmentioning

confidence: 99%

Thiol dioxygenase turnover yields benzothiazole products from 2-mercaptoaniline and O2-dependent oxidation of primary alcohols

Morrow

Sardar

Thapa

et al. 2017

Archives of Biochemistry and Biophysics

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Thiol dioxygenases are non-heme mononuclear iron enzymes that catalyze the O2-dependent oxidation of free thiols (-SH) to produce the corresponding sulfinic acid (-SO2−). Previous chemical rescue studies identified a putative FeIII-O2•− intermediate that precedes substrate oxidation in Mus musculus cysteine dioxygenase (Mm CDO). Given that a similar reactive intermediate has been identified in the extradiol dioxygenase 2, 3-HCPD, it is conceivable that these enzymes share other mechanistic features with regard to substrate oxidation. To explore this possibility, enzymatic reactions with Mm CDO (as well as the bacterial 3-mercaptopropionic acid dioxygenase, Av MDO) were performed using a substrate analogue (2-mercaptoaniline, 2ma). This aromatic thiol closely approximates the catecholic substrate of homoprotocatechuate of 2, 3-HPCD while maintaining the 2-carbon thiol-amine separation preferred by Mm CDO. Remarkably, both enzymes exhibit 2ma-gated O2-consumption; however, none of the expected products for thiol dioxygenase or intra/extradiol dioxygenase reactions were observed. Instead, benzothiazoles are produced by the condensation of 2ma with aldehydes formed by an off-pathway oxidation of primary alcohols added to aqueous reactions to solubilize the substrate. The observed oxidation of 1°-alcohols in 2ma-reactions is consistent with the formation of a high-valent intermediate similar to what has been reported for cytochrome P450 and mononuclear iron model complexes.

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Section: Resultsmentioning

confidence: 99%

Thiol dioxygenase turnover yields benzothiazole products from 2-mercaptoaniline and O2-dependent oxidation of primary alcohols

Morrow

Sardar

Thapa

et al. 2017

Archives of Biochemistry and Biophysics

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“…performed the aerial oxidation of aromatic primary amines ( 81 ) and 4 , by using 5 mol % of Fe (NO 3 ) 3 and TEMPO (2,2,6,6‐tetramethyl‐1‐piperidinyloxyl) as a catalyst and air as a green oxidant. They fetched numerous benzimidazole moieties ( 82 ) in 83–93% yield at 110°C under solvent‐free conditions in 24–30 h (Scheme , Table , entry 1) . While in a similar attempt by this group, target product 84 was synthesized by aerial oxidation of reactants, benzyl alcohols ( 83 ), and o ‐phenylenediamines ( 4 ) in 69–85% yield under solvent‐free conditions.…”

Section: Oxidative Coupling Of O‐phenylenediamine Using Transition Mementioning

confidence: 99%

Recent Trends in the Synthesis of Benzimidazoles From o‐Phenylenediamine via Nanoparticles and Green Strategies Using Transition Metal Catalysts

Singhal

Khanna

Panda

et al. 2019

Journal of Heterocyclic Chem

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Benzimidazole is a heterocyclic moiety of immense importance as it acts as a primary “biolinker” in diverse synthetic routes to obtain bioactive compounds. Substituted benzimidazoles are known to possess a varied range of pharmacological applications, namely, anti‐cancer, anti‐diabetic, anti‐inflammatory, and antiviral like anti‐HIV and anti‐fungal. A number of reviews covering the important aspects of benzimidazoles such as pharmacological activities, SAR studies, and well‐known methods of synthesis have appeared in the literature. However, green synthetic methods particularly using transition metal (TM) catalysts and their nanoparticles, although being more viable and extensively applied by researchers in the present scenario, have not been exclusively and expansively reviewed. Besides this, the vital precursors required for knitting the skeleton of benzimidazole are mainly o‐aryldiamines. The conventional synthesis generally involved the condensation of these diamines with carbonyl/carboxylic acid derivatives either via high temperature heating or via adding strong acids, mostly resulting in poor yields or mixtures. However, recent trends are replacing these conditions by mild and green conditions through TM catalysts. Therefore, the current review emphasizes on the recent trends adopted in the synthesis of benzimidazoles using condensation reaction of o‐phenylenediamines and various aldehydes/ester/amide/alcohols with TM in a catalytic role in nanoform and under environmentally benign green conditions.

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“…Inspired by the iron-mediated catalytic system reported by Xu and co-workers for the preparation of imines through aerobic oxidative coupling of amines under air, 21 Lu and co-workers demonstrated that the aerobic oxidative cyclocondensation of benzylic primary amines (1.2 equiv) and o-phenylenediamine (1 equiv) can be achieved by the synergistic combination of Fe(NO 3 ) 3 (5 mol%) and electron-deficient 2,2,6,6-tetramethylpiperidin-1-yloxy radical (TEMPO) (5 mol%), under solvent-free conditions in air. 22 Variously substituted benzylic amines were converted into 2-substituted benzimidazoles in high yields (78-93%) at 110 °C for 24-28 hours. The first step of the proposed reaction mechanism consists of the aerobic Fe/TEMPO-catalyzed oxidation of benzylic amine to the corresponding benzylimine intermediate in a way reminiscent of that reported by Hu and Kerton for the aerobic Cu/TEMPO-catalyzed version (Scheme 9).…”

Section: Scheme 8 Possible Pathways For the Copper-catalyzed Aerobic mentioning

confidence: 99%

Recent Advances in the Synthesis of Benzimidazole Derivatives from the Oxidative Coupling of Primary Amines

Largeron

Nguyen²

2017

Synthesis

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Benzimidazole belongs to the top five most commonly used five-membered aromatic nitrogen heterocycles among U.S. FDA approved pharmaceuticals. Over the last few years, a large number of improved synthetic strategies have been developed to construct the benzimidazole molecular framework under environmentally benign conditions. This review focuses on the use of primary amines as readily available substrates for the synthesis of benzimidazole derivatives through different types of oxidative cross-coupling reactions.1 Introduction2 Catalyst-Free Oxidative Coupling of Primary Amines3 Catalytic Oxidative Coupling of Primary Amines3.1 Metal-Catalyzed Reactions3.2 Metal-Free Catalyzed Reactions3.3 Bioinspired Catalyzed Reactions4 Conclusion

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Iron-Catalyzed Highly Efficient Aerobic Oxidative Synthesis of Benzimidazoles, Benzoxazoles, and Benzothiazoles Directly from Aromatic Primary Amines Under Solvent-Free Conditions in the Open Air

Cited by 32 publications

References 28 publications

Thiol dioxygenase turnover yields benzothiazole products from 2-mercaptoaniline and O2-dependent oxidation of primary alcohols

Thiol dioxygenase turnover yields benzothiazole products from 2-mercaptoaniline and O2-dependent oxidation of primary alcohols

Recent Trends in the Synthesis of Benzimidazoles From o‐Phenylenediamine via Nanoparticles and Green Strategies Using Transition Metal Catalysts

Recent Advances in the Synthesis of Benzimidazole Derivatives from the Oxidative Coupling of Primary Amines

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