T. A. Kuz'menko

1,2,4-Triazolo[1,5-a]benzimidazoles: Tautomerism and alkylation

The position of the tautomeric equilibrium in unsubstituted 1,2,4-triazolo[1,5-a] benzimidazole, as well as in its 2-methyl and 2-phenyl derivatives, was investigated by UV, IR, and PMR spectroscopy and by determination of the ionization constants. In all cases the amount of the 4H tautomer in the equilibrium mixture is two to three orders of magnitude greater than the amount of the 3H tautomer, while signs of the existence of the 1 H form are not observed. The synthesis of unsubstituted triazolo [1,5-a]-benzimidazole was accomplished for the first time. The alkylation of the indicated triazolo [1,5-a]benzimidazoles was studied and a relationship between the regiospecificity of this reaction and the position of the tautomeric equilibrium was established.

Synthesis and some conversions of N-substituted benzimidazole-2-sulfonic acids

A series of N-substituted benzimidazole-2-sulfonic acids was synthesized in good yield by the N-alkylation of benzimidazole-2-sulfonic acids by alkylation with simple and functionalized alkylating agents under mild conditions. The corresponding N-substituted benzimidazolones and also primary, secondary, and tertiary amines were obtained by the action on the obtained compounds of alkali, ammonia, ammonium acetate, and amines.

Cyclization of 3-Ethoxycarbonylmethyl-, 3-Cyanomethyl-, and 3-Acetylmethyl-1-amino-2-methylbenzimidazolium Salts Effected by Acetic Anhydride in the Presence of a Base

Abstract3-Ethoxycarbonylmethyl- and 3-cyanomethyl-1-amino-2-methylbenzimidazolium chlorides cyclized at treatment with acetic anhydride in the presence of potassium carbonate to afford a mixture of derivatives of pyrazolo[1,5-a]benzimidazole and 4-aminopyrrolo[1,2-a]benzimidazole. Therewith in the first case prevails the process of pyrazole ring fusion, and in the latter pyrrole ring is fused. 3-Aroyl(thenoyl)methyl-1-amino-2-methylbenzimidazolium bromides under the same conditions are converted into 1-aroyl(thenoyl)-2-methyl- and 2-4-acetamido-3-acetylpyrrolo[1,2-a]benzimidazoles.

1-Amino-3-alkyl-2-(methylthio)benzimidazolium salts: synthesis, reaction with CH-acid anions, and conversion to pyrazolo[1,5-a]benzimidazole derivatives

For the first time, 1-amino-3-alkylbenzimidazolinethiones were obtained by heating 1-amino-3-alkylbenzimidazolium iodides with sulfur in the presence of triethylamine. They were converted to 1-amino-3-alkyl-2-(methylthio)benzimidazolium salts, which, during reaction with CH-acid onions, gave the corresponding 1-amino-3-alkyl-2-methylenebenzimidazoline derivatives. Under conditions of alkaline or acid catalysis, the latter derivatives cyclized to 2-amino- or 2-hydroxy derivatives of pyrazolo[1,5-a]benzimidazole.

3-α-Halocarbonyl derivatives of pyrazolo[1,5-a] benzimidazole and their reactions

Abstract3-(α-haloacyl)-2,4-dialkylpyrazolo[1,5-a]benzimidazoles can be obtained either by brominating 3-acetylpyrazolo[1,5-a]benzimidazoles with bromine in acetic acid, or by acylating the 3-unsubstituted pyrazolobenzimidazoles with haloacetic halides. Halogenation of 3-acetylpyrazolo[1,5-a]benzimidazoles with bromine in acetic acid in the presence of sodium acetate, and bromination with N-bromosuccinimide or 1-chlorobenzotriazole, result in deacylation to give 3,6(7)-dibromo- and 3-chloropyrazolo[1,5-a]benzimidazoles. The mono- and trihaloketones obtained have been used to prepare the corresponding aminoketones, the 3-carboxylic acid, and its derivatives.

1-Amino-2-alkylaminobenzimidazoles and their reactions with carbonyl-containing compounds

Abstract1-Amino-2-alkylaminobenzimidazoles were synthesized by a reaction involving exchange of the sulfo group in 1-aminobenzimidazole-2-sulfonic acid. 3-Alkyl-3H-1, 2,4-triazolo [1,5-a] benzimidazoles and 4-alkyl-4H-1,2,4-triazinol[2,3-a]benzimidazol-3-ones were obtained on the basis of them.

Unusual cleavage of phenacyl-substituted benzimidazolium salts. Synthesis of 1,4-diarylimidazoles

The action of ammonium acetate in acetic acid on 1-alkyl(aralkyl)-3-phenacylbenzimidazolium bromides leads, in addition to the formation of a new imidazole ring, to cleavage of the benzimidazole fragment of the molecule at the 1,2 bond to give 1-alkyl(aralkyl)aminoaryl-4-arylimidazoles. 1,2-Dimethyl-3-(p-nitrophenacyl)benzimidazolium bromide is converted under similar conditions to the corresponding 2-methylimidazole. 4,4′-Dimethyl-2,2′-bis(p-nitrophenyl)-1,1′-dipyrrolo[1,2-a]benzimidazole was isolated as a side product of this reaction.

Synthesis and deamination of 9-aminoimadazo[1,2-a]benzimidazoles

The reaction between 1,2-diaminobenzimidazole and α-halocarbonyl compounds has given some novel 9-aminoimidazo [1,2-a]benzimidazoles. On treatment with nitrous acid or potassium hydroxide in DMSO, these compounds give, in addition to the deaminated compounds, 3-nitroso-derivatives of the deamination products. In the system DMSO-KOH, 9-benzylideneaminoimidazobenzimidazoles are converted smoothly into 1(9H)-imidazobenzimidazoles. It is shown that 3-nitroso-derivatives which are unsubstituted in the NH group exist predominantly in the hydroxyimino form.

Reaction of N-aminobenzimidazolium cations with aromatic aldehydes. Synthesis of 2,4-diaryl-as-triazino[1,6-a] benzimidazoles

On heating with aromatic or heteroaromatic aldehydes in polar aprotic solvents, 1-amino-3-alkylbenzimidazolium salts form 2,4-diaryl derivatives of a new heterocyclic system of as-triazino[1,6-a]benzimidazole.

Research on imidazo[2,1-a]isoquinoline derivatives. 3. Acylation of 2-substituted imidazo[2,1-a]isoquinolines

The acylation of 2-alky1, 2-aryl, and 2-hetaryl derivatives of imidazo[2,1-a]isoquinoline was studied. 3-Acetyl-substituted derivatives of this system were synthesized by the action of acetic anhydride on 2-arylimidazoisoquinolines in the presence of magnesium perchlorate. Under similar conditions 2-hetaryl derivatives are acetylated not only in the 3 position but also in the hetaryl ring. 3-Acetyl-2-methylimidazoisoquinoline, which is not formed as a result of direct acylation, was synthesized by indirect methods, viz., on the basis of 1-aminoisoquinoline and 3-chloroacetylacetone or from 1-acetamidoisoquinoline and bromoacetone. The compounds obtained are extremely resistant to hydrolysis, give the usual reactions at the carbonyl group, condense with aromatic aldehydes, and undergo bromination to give 3-bromo- and 3-dibromoacetyl derivatives.