Isomerization in the Oxidative Cyclocondensation of 2-Aroylmethyl-1H-benzimidazoles with o-Aminothiophenol

Dzvinchuk, I. B.; Vypirailenko, A. V.; Lozinskii, M. O.

doi:10.1023/b:cohc.0000048295.31636.0d

Cited by 4 publications

(3 citation statements)

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“…6 In view of these multifarious useful applications, many efforts have been made to develop synthetic access to 1,4-benzothiazines. The most commonly used methods are three types including (1) the reaction of 2-aminobenzenethiols with a-haloketones or a-haloesters; 7 (2) the oxidative cyclocondensation of 2-aminobenzenethiols with 1,3-dicarbonyl compounds through key disulfides formation process using dimethylsulfoxide as oxidant, 8 aerial oxidation 9 in solvent-free system using hydrazine hydrate as catalyst, or using microwave 10 technique; (3) the oxidative ring expansion of N-substituted benzothiazolines in refluxing dimethylsulfoxide under nitrogen atmosphere, 11 in toluene or dichloromethane using sulfuryl chloride as oxidant, 12 or in toluene/tBuOK using iodine as oxidant. 13 Our finding belongs to the oxidative ring expansion category, which prompted us to further investigate the oxidative properties of benzothiazolylacetate in order to extend the utility of this m-CPBA-mediated method since none of the oxidative ring expansion methods has been reported to afford 3-unsubstituted 1,4-benzothiazine under such simple reaction systems.…”

Section: Introductionmentioning

confidence: 99%

The facile synthesis of benzothiazolylideneacetates and 1,4-benzothiazines through a highly controllable oxidation of benzothiazolylacetates

Liu

et al. 2009

Tetrahedron Letters

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Section: Introductionmentioning

confidence: 99%

The facile synthesis of benzothiazolylideneacetates and 1,4-benzothiazines through a highly controllable oxidation of benzothiazolylacetates

Liu

et al. 2009

Tetrahedron Letters

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“…The first is found at 7.39-7.50 and the second at 7.19-7.30 ppm. We have previously observed features related to the orthogonal orientation of the aryl substituent relative to the heterocyclic plane and hindrance to proton exchange between benzimidazole nitrogen atoms in the spectra of structural analogs of compounds 3a-g containing a partially hydrogenated pyrimidine or 1,4-benzothiazine ring [9,10] in place of the pyridazine ring. When compared with the H-1 signal at 10.80-11.18 ppm the H-2' signal in 3a-g is at higher field (10.15-10.43 ppm), it is less broadened, and its intensity is decreased less significantly after addition of D 2 O.…”

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confidence: 99%

Synthesis and aromatization of 2-(3,6-diaryl-2,5-dihydropyridazin-4-yl)-1H-benzimidazoles

Dzvinchuk

Nesterenko

Lozinskii

2008

Chem Heterocycl Comp

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We have previously reported the methodology of synthesizing novel benzimidazole derivatives based on 2-phenacyl-1H-benzimidazoles [1,2]. In particular, C-alkylation of the latter using phenacyl bromides gave the 1,4-diaryl-2-(1H-benzimidazol-2-yl)butane-1,4-diones 1a-g [3]. It is known [4] that 1,4-diketones can undergo cyclocondensation with hydrazine to form dihydropyridazines which are readily oxidized to pyridazines. Similar reactions of the 2-hetaryl-1,4-diketones of type 1 were unknown and are studied in this work.We have found that the cyclocondensation of compounds 1a-g with hydrazine hydrate occurs upon heating in a mixture of ethanol and pyridine and is accompanied by 1,3-migration of a proton from the methine group to the nitrogen atom in a direction leading not to compounds 2a-g with a 1,3-dihydrobenzimidazole fragment but to the 2-(3,6-diaryl-2,5-dihydropyridazin-4-yl)-1-benzimidazoles 3a-g. These products are obtained in 87-97% yields and are selectively oxidized by nitrous acid in pyridine (75-80ºC) undergoing aromatization to give 82-96% yields of the 2-(3,6-diarylpyridazin-4-yl)-1H-benzimidazoles 4a-g (compounds 4a,d,g crystallize in the form of molecular compounds with acetic acid with the compositions 4a·AcOH, 4d·AcOH, and 4g·AcOH).Evidently the formation of compounds of type 3 and their relative stability (they are not oxidized significantly when recording the NMR spectra in DMSO-d 6 ) is connected to the presence of an energetically favored conjugative chain in which the NH group of the dihydropyridazine ring is a donor and the benzimidazole fragment an acceptor of electrons. The conjugated chain constitutes a chromophoric system thus making compounds 3a-f yellow and the compound 3g with a nitrophenyl substituent orange colored. According to literature data, structural analogs of compound 3a with a Ph or Me group in place of the benzimidazole fragment are colorless [5,6] and with a C≡N group yellow [7]. We have found that, even with excess hydrochloric acid, the product 3a forms the orange mono hydrochloride 5 in which the dihydropyridazine ring can be involved in the delocalization of the positive charge (see the limiting structure 5"). Treatment of the salt 5 with ammonia regenerates the starting base 3a.

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“…Literature survey shows many different protocols that have been developed for the synthesis of 1,4-benzothiazines. [2][3][4][5][6][7][8][9] The most commonly employed methods involve the reaction of 2,3-dihydro-1,3-benzothiazoles with sulfuryl chloride, in toluene, 4 in anhydrous dichloromethane under nitrogen atmosphere, 5 by the oxidative cyclocondensation of 2-aroylmethyl-1H-benzimidazoles with o-aminothiophenol, in which a mixture of DMSO, acetic acid and water is used as oxidant and solvent giving isomeric product, 6 by the oxidative ring expansion of N-substituted benzothiazolines in refluxing dimethylsulfoxide under nitrogen atmosphere. 7 This straightforward method suffers from low yields due, in part, to competitive benzothiazoline thermal decomposition in which 2-substituted benzothiazoles were formed.…”

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Synthesis of a Series of 2,3-Disubstituted 4H-1,4-Benzothiazines and X-ray Crystal Structure of Ethyl 7-Chloro-3-Methyl-4H-1,4-Benzothiazine-2-Carboxylate

Dandia

Sarawgi

Hursthouse

et al. 2006

Journal of Chemical Research

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The reaction between 2-aminobenzenethiol and ethyl acetoacetate is studied under a variety of conditions, and a procedure for the exclusive synthesis of 1,4-benzothiazines by the neat reaction of substituted aminothiols with bketoesters and b-dicarbonyl compounds in 85-96% yield is described. With microwave heating, even when both the reactants are solid, yields are high, reaction times brief, and work-up easy. A facile reaction is also observed even in a solid-state reaction. The molecular structure of ethyl 7-chloro-3-methyl-4H-1,4-benzothiazine-2-carboxylate (4d) was determined by single-crystal X-ray diffraction.

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Isomerization in the Oxidative Cyclocondensation of 2-Aroylmethyl-1H-benzimidazoles with o-Aminothiophenol

Cited by 4 publications

References 1 publication

The facile synthesis of benzothiazolylideneacetates and 1,4-benzothiazines through a highly controllable oxidation of benzothiazolylacetates

The facile synthesis of benzothiazolylideneacetates and 1,4-benzothiazines through a highly controllable oxidation of benzothiazolylacetates

Synthesis and aromatization of 2-(3,6-diaryl-2,5-dihydropyridazin-4-yl)-1H-benzimidazoles

Synthesis of a Series of 2,3-Disubstituted 4H-1,4-Benzothiazines and X-ray Crystal Structure of Ethyl 7-Chloro-3-Methyl-4H-1,4-Benzothiazine-2-Carboxylate

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