I. B. Dzvinchuk

2-Phenacylbenzothiazole in the Biginelli Reaction

The cyclocondensation of 2-phenacylbenzothiazole with aromatic aldehydes and urea or thiourea in the Biginelli reaction gave previously unreported 4-aryl-5-(2-benzothiazolyl)-2-oxo-6-phenyl-1,2,3,4-tetrahydropyrimidines and their 2-thioxo analogs. An efficient procedure was developed for carrying out the three-component reaction at low temperatures. The structure peculiarities of the products were analyzed using IR, 1H NMR, and X-ray diffraction data.

2-Acylmethyl-1H-benzimidazoles in the Biginelli Reaction

By cyclocondensation of 2-acylmethyl-1H-benzimidazoles with aromatic aldehydes and urea according to the Biginelli reaction, we have obtained previously unknown 6-substituted 4-aryl-5-(2-benzimidazolyl)-2-oxo-1,2,3,4-tetrahydropyrimidines. We have developed an efficient procedure for conducting the three-component reaction at fairly low temperatures. We have analyzed the structural features of the synthesized compounds based on 1H NMR spectra and IR spectroscopy.

Selective recyclization of 2-aroylmethyl-1H-benzimidazole hydrazones by condensation with dimethylformamide

Abstract2-Aroylmethyl-1H-benzimidazole hydrazones are converted to 1-[pyrazol-3(5)-yl]benzimidazoles by refluxing in dimethylformamide in the presence of trifluoroacetic acid. The same products are obtained by refluxing 2-aroylmethyl-1H-benzimidazoles with hydrazine hydrochloride in dimethylformamide. Electron donor substituents in the para position of the aryl fragment of the starting compounds do not favor the reaction.

Synthesis of pyrido[1,2-a]benzimidazoles from 2-acylmethyl-1H-benzimidazoles

Methods are proposed for the synthesis of previously unknown pyrido[1,2-a]benzimidazoles via the cyclocondensation of 2-acylmethyl-1H-benzimidazoles with malononitrile, triethylorthoformate ester, or ethoxymethylenemalononitrile.

Hydrazinolytic recyclization of 2-phenacylbenzothiazole

Hydrazinolytic recyclization of 2-phenacylbenzothiazole proceeds via cleavage of the C—S bond in the ring and is accompanied by oxidation of resulting 2-[(5-phenylpyrazole-3-yl)amino]thiophenol into the corresponding disulfide. The subsequent intramolecular cyclocondensation gives selectively pyrazolo[4,3-b][1,4]benzothiazines.

Synthesis of 2-(1,2,3-Thiadiazol-5-yl)-1H-benzimidazoles

We have developed a convenient preparative method for synthesis of previously unknown 2-(1,2,3-thiadiazol-5-yl)-1H-benzimidazoles based on reaction of benzoylhydrazones of 2-acylmethyl-1H-benzimidazoles with thionyl chloride.

Synthesis of 2-(3-Indolyl)-1H-benzimidazoles from 2-Acylmethyl-1H-benzimidazoles

The interaction of 2-acetyl(aroyl)methyl-1H-benzimidazoles with phenylhydrazine on heating in trifluoroacetic acid proceeds by a type of Fischer reaction with the formation of 2-[2-methyl(aryl)-3-indolyl]-1H-benzimidazoles.

Isomerization of 2-Phenacyl-1H-benzimidazole Arylhydrazones to 1-Aryl-5-(o-aminoanilino)-3-phenylpyrazoles by Trifluoroacetylation and Hydrazinolysis

A convenient preparative two-stage method was developed for the isomerization of 2-phenacyl-1H-benzimidazole arylhydrazones to previously unknown 5-(o-aminoanilino)-1-aryl-3-phenylpyrazoles. The transformation scheme includes recyclization during acylation with trifluoroacetic anhydride leading to the formation of 1-aryl-3-phenyl-5-(o-trifluoroacetylaminoanilino)pyrazoles, which then undergo hydrazinolysis.

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

Oxidative cyclocondensation of 2-aroylmethyl-1H-benzimidazoles with o-aminothiophenol gave the previously unknown 3-aryl-2-(2-benzimidazolyl)-4H-1,4-benzothiazines and (or) the isomeric 2H-1,4-benzothiazines. 2-(4-Nitrophenacyl)-1H-benzimidazole and 2-phenacylbenzothiazole gave 4H-1,4-benzothiazines which are not liable to isomerize but the reaction of the first compound is complicated by a hydrolytic fission which yields 2-[2-(4-nitrobenzoylamino)phenylthiomethyl]benzimidazole. A mixture of dimethylsulfoxide, acetic acid, and water was used as oxidant and solvent. The effect of the substituent and of the solvent on the tendency of the products to undergo prototropic isomerization in the benzothiazine ring have been studied.

Synthesis of 2-(3-furyl)-1H-benzimidazoles from 2-phenacyl-1H-benzimidazoles

C-Alkylation at the active methylene group of 2-phenacyl-1H-benzimidazoles with phenacyl bromides proceeds highly selectively with the formation of the corresponding 1,4-diketones, which on heating with hydrochloric acid are cyclized with the formation of the previously unknown 2-(2,5-diaryl-3-furyl)-1H-benzimidazoles.