- Nickel catalyzed sustainable synthesis of benzazoles and purines: Via acceptorless dehydrogenative coupling and borrowing hydrogen approach
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Herein we report nickel-catalyzed sustainable synthesis of a few chosen five-membered fused nitrogen heterocycles such as benzimidazole, purine, benzothiazole, and benzoxazole via acceptorless dehydrogenative functionalization of alcohols. Using a bench stable, easy to prepare, and inexpensive Ni(ii)-catalyst, [Ni(MeTAA)] (1a), featuring a tetraaza macrocyclic ligand (tetramethyltetraaza[14]annulene (MeTAA)), a wide variety of polysubstituted benzimidazole, purine, benzothiazole, and benzoxazole derivatives were prepared via dehydrogenative coupling of alcohols with 1,2-diaminobenzene, 4,5-diaminopyrimidine, 2-aminothiphenol, and 2-aminophenol, respectively. A wide array of benzimidazoles were also prepared via a borrowing hydrogen approach involving alcohols as hydrogen donors and 2-nitroanilines as hydrogen acceptors. A few control experiments were performed to understand the reaction mechanism.
- Chakraborty, Gargi,Guin, Amit Kumar,Mondal, Rakesh,Paul, Nanda
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p. 7217 - 7233
(2021/08/30)
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- Visible-light-induced condensation cyclization to synthesize benzimidazoles using fluorescein as a photocatalyst
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A mild strategy for visible-light-induced synthesis of benzimidazoles was developed using aromatic aldehydes and o-phenylenediamines as substrates. The use of an organic dye, fluorescein, as an innoxious photocatalyst provided a mild and inexpensive catalytic system to synthesize a series of benzimidazoles in moderate to excellent yields. It was originally applied to this system to obtain benzimidazoles. Besides, the catalytic system does not require an additional oxidant or metal which was good for the environment.
- Li, Zhuofei,Song, He,Guo, Rui,Zuo, Minghui,Hou, Chuanfu,Sun, Shouneng,He, Xin,Sun, Zhizhong,Chu, Wenyi
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p. 3602 - 3605
(2019/07/09)
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- Unmodified Fe3O4 nanostructure promoted with external magnetic field: safe, magnetically recoverable, and efficient nanocatalyst for N- and C-alkylation reactions in green conditions
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Transition metal compounds have emerged as suitable catalysts for organic reactions. Magnetic compounds as soft Lewis acids can be used as catalysts for organic reactions. In this report, the Fe3O4 nanostructures were obtained from Fe2+ and Fe3+-salts, under an external magnetic field (EMF) without any protective agent. The X-ray photoelectron spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy tools were used to characterize these magnetic compounds. The two-dimensional (2-D, it showed nanometric size in the two dimensions, nanorod structure) Fe3O4 compound showed high catalytic activity and stability in N- and C-alkylation reactions. A diverse range of N- and C-alkylation products were obtained in moderate to high yield under green and mild conditions in air. Also the N- and C-alkylation products can be obtained with different selectivity and yield by exposure reactions with EMF. Results of alkylation reactions showed that the presence of Fe(II) and Fe(III) species on the surface of magnetic catalysts (phase structure of magnetic compounds) are essential as very cheap active sites. Also, morphology of magnetic catalysts had influence on their catalytic performances. After the reaction, the catalyst/product(s) separation could be easily achieved with an external magnet and more than 95% of catalyst could be recovered. The catalyst was reused at least four times without any loss of its high catalytic activity for N- and C-alkylation reactions.
- Rafiee, Ezzat,Joshaghani, Mohammad,Abadi, Parvaneh Ghaderi-Shekhi
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p. 2503 - 2522
(2018/01/04)
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- Iron-catalyzed highly efficient aerobic oxidative synthesis of benzimidazoles direct from oximes in water
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This article presents a general and efficient method for aerobic oxidative synthesis of benzimidazoles from oximes catalyzed by Fe(NO3)3·9H2O under air in water. This practical method uses air as an economic and green oxidant, water as a green solvent, and tolerates a wide range of substrates that can afford the target benzimidazoles in moderate to good yields.
- Yu, Jiatao,Lu, Ming
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p. 471 - 479
(2016/04/26)
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- An efficient and environmental benign synthesis of 2-benzimidazoles and 2-benzothiazoles using CeCl3-NaI as catalyst
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A one-pot condensation of an aldehyde with 1,2-phenylenediamine or 2-aminothiophenol in dimethyl carbonate at 100°C under O2 in the presence of catalytic amounts of CeCl3-NaI gave an imine intermediate, which cyclised and dehydrogenated to give 2-arylbenzimidazoles or 2-arylbenzothiazoles in good yields.
- Zhu, Xun,Wei, Yunyang
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p. 119 - 121
(2013/04/23)
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- Unprecedented reaction between ethyl α-cyanocinnamate and o-phenylenediamine: Development of an efficient method for the transfer hydrogenation of electronically depleted olefins
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A reaction between ethyl α-cyanocinnamate and o-phenylenediamine under thermal conditions yielded 2-cyano-3-phenyl-propionic acid ethyl ester, 2-phenyl benzimidazole, and ethyl cyanoacetate. The mechanistic revelations led to the development of a simple and efficient transfer-hydrogenation process from the in situ generated benzimidazolines to activated olefins under solventless and catalyst-free conditions. Georg Thieme Verlag Stuttgart.
- Kumar, Satish,Kapoor, Kamal K.
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p. 2809 - 2814
(2008/02/13)
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- Reactivities of acridine compounds in hydride transfer reactions
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Reactivities of acridine derivatives (10-benzylacridinium ion, 1a +, 10-methylacridinium ion, 1b+, and 10-methyl-9- phenylacridinium ion, 1c+) have been compared quantitatively for hydride transfer reactions with 1,3-dimethyl-2-substituted phenylbenzimidazoline compounds, 2Ha-h. Reactions were monitored spectrophotometrically in a solvent consisting of four parts of 2-propanol to one part of water by volume at 25 ± 0.1°C. Reduction potentials have been estimated for acridine derivatives by assuming that the equilibrium constants for the reductions of 1a+-c+ by 2Hb would be the same in aqueous solution and accepting -361 mV as the reduction potential of the 1-benzyl-3- carbamoylpyridinium ion. The resulting reduction potentials, E redo, are -47 mV for 1a+, -79 mV for 1b +, and -86 mV for 1c+. Each of acridine derivatives gives a linear Bronsted plot for hydride transfer reactions. The experimental slopes were compared with those obtained by Marcus theory. This comparison shows that the kinetic data are consistent with a one-step mechanism involving no high-energy intermediates. Copyright
- Lee, In-Sook Han,Kil, Hyun Joo,Ji, Young Ran
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p. 484 - 490
(2008/02/07)
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