Palladium-catalyzed N-heteroannulation of N-allyl- or N-benzyl-2-nitrobenzenamines: synthesis of 2-substituted benzimidazoles

Hubbard, Jeremiah W.; Piegols, Adam M.; Söderberg, Björn C.G.

doi:10.1016/j.tet.2007.05.010

Cited by 46 publications

(15 citation statements)

References 56 publications

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“…On the other hand, the same group succeeded in preparing benzimidazoles by a reaction involving a methylene group in the alpha position with respect to the amino group. The only requisite is that the methylene group should be activated by being in an allylic or benzylic position (Scheme ) …”

Section: Synthesis Of N‐heterocycles By Intra‐molecular Cyclization Rmentioning

confidence: 99%

“…The only requisite is that the methylene group should be activated by being in an allylic or benzylic position (Scheme 29). [134] Best results were obtained by working in DMF with only phenanthroline as ligand for palladium and 6 atm CO. Electronwithdrawing and electrondonating substituents are tolerated both on the aryl ring containing the nitro group and, when present, on the benzylic ring.…”

Section: Synthesis Of Other 5-membered N-heterocyclesmentioning

confidence: 99%

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Transition Metal Catalyzed Reductive Cyclization Reactions of Nitroarenes and Nitroalkenes

2019

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Nitroarenes are the entry point for the production of most nitrogen‐containing aromatic compounds. Thus, any transformation that leads directly from them to the final product allows saving one or more synthetic steps. This review deals with homogeneously catalyzed reactions leading to the formation of N‐heterocyclic compounds from nitroarenes or nitroalkenes in one pot. Reactions that lead to the intermediate formation of amines are not considered. Carbon monoxide is the most often employed reductant because it allows selective reactions, is cheap, and only produces CO2 as stoichiometric byproduct. However, the difficulty in handling pressurized CO has stimulated in recent years the development of CO‐surrogates, that is molecules able to liberate CO during the reaction. The use of phosphines and diols has also been developed in conjunction with molybdenum catalysts. The review focusses in more detail on the literature in the period 2006–2018, but reference to earlier work is made when necessary to put recent results in a more general context.

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Section: Synthesis Of N‐heterocycles By Intra‐molecular Cyclization Rmentioning

confidence: 99%

Section: Synthesis Of Other 5-membered N-heterocyclesmentioning

confidence: 99%

Transition Metal Catalyzed Reductive Cyclization Reactions of Nitroarenes and Nitroalkenes

2019

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“…FeCl 3 · 6 H 2 O (0.013 g, 0.05 mmol) and activated charcoal (0.13 g, 11 mmol) were added to a soln. of methyl 2-(benzylamino)-3-nitrobenzoate (15 [19]; 1.0 g, 3.5 mmol) in a mixture of MeOH (15 ml) and freshly distilled THF (15 ml), according to a known procedure [20]. After refluxing for 30 min, a soln.…”

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confidence: 99%

Physicochemical Profiling of Sartans: A Detailed Study of Ionization Constants and Distribution Coefficients

Tosco

Rolando

Fruttero

et al. 2008

Helvetica Chimica Acta

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A detailed investigation of the ionization and lipophilicity profiles of selected sartans (valsartan, losartan, irbesartan, candesartan, candesartan cilexetil), a class of antihypertensives commonly used in therapy, is presented. The pK a macroconstants were determined by integrated potentiometry, capillary electrophoresis, and UV spectrophotometry. The measured pK a macroconstants were connected with the ionizable centers present in each molecule with the aid of model compounds. Potentiometric titrations with the GLpKa apparatus were performed to determine the distribution profile (log D vs. pH) of valsartan, while the shake-flask procedure was used to characterize the distribution profile of the other compounds. Valsartan showed a lipophilicity profile consistent with the presence of two acidic centers. Losartan and irbesartan, which contain one acidic and one basic center, displayed the classical bellshaped profile of ordinary ampholytes. By contrast, a more complex situation emerged in the case of candesartan, due to the large number of ionization equilibria involved. The low solubility of candesartan cilexetil, together with the ease of hydrolysis of the ester moiety, prevented a successful investigation of its ionization and lipophilicity profiles.

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“…The synthesis of substituted benzimidazoles involves the construction of the imidazole ring via cyclization of appropriate N -substituted dinitroanilines by using sodium hydroxide in aqueous dioxane [2] or palladium catalysis [3]. In addition, the cyclization of N -substituted nitroanilines has been accomplished under thermal and photochemical conditions [4,5].…”

Section: Introductionmentioning

confidence: 99%

Deprotonated N-(2,4-dinitrophenyl)amino acids undergo cyclization in solution and the gas phase

George

Ramesh²,

Srinivas³

et al. 2011

International Journal of Mass Spectrometry

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The collisionally activated mass spectral fragmentations of N-(2,4-dinitrophenyl)alanine and phenylalanine [M – H]- may be gas-phase analogs of the base-catalyzed cyclization of N-(2,4-dinitrophenyl)amino acids in aqueous dioxane. This latter reaction is one source of the 2-substituted 5-nitro-1H-benzimidazole-3-oxides, which are antibacterial agents. The fragmentation of both compounds, established by tandem mass spectrometric experiments and supported by molecular modeling using DFT methods, indicate that the [M - H]- ions dissociate via sequential eliminations of CO2 and H2O to produce deprotonated benzimidazole-N-oxide derivatives. The gas-phase cyclization reactions are analogous to the base-catalyzed cyclization in solution, except that in the latter case, the reactant must be a dianion for the reaction to occur on a reasonable time scale. The cyclization of N-(2-nitrophenyl)phenylalanine, which has one less nitro group, requires a stronger base for the cyclization than the compound with a second nitro group at the 4-position. Following losses of CO2 and H2O are expulsions of both neutral molecules and free radicals, the latter being examples of violations of the even-electron ion rule.

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Palladium-catalyzed N-heteroannulation of N-allyl- or N-benzyl-2-nitrobenzenamines: synthesis of 2-substituted benzimidazoles

Cited by 46 publications

References 56 publications

Transition Metal Catalyzed Reductive Cyclization Reactions of Nitroarenes and Nitroalkenes

Transition Metal Catalyzed Reductive Cyclization Reactions of Nitroarenes and Nitroalkenes

Physicochemical Profiling of Sartans: A Detailed Study of Ionization Constants and Distribution Coefficients

Deprotonated N-(2,4-dinitrophenyl)amino acids undergo cyclization in solution and the gas phase

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