M. M. El'chaninov

Investigations of 2-substituted imidazoles. 2. Synthesis and electrophilic substitution of 1-methyl-2-(thienyl-2)imidazole. A convenient method of methylation of 2-R-imidazoles

We have synthesized 2-(thienyl-2)imidazole and its N-methyl derivative. The latter product was obtained by nitration, bromination, acylation, and formylation, occurring as a rule on the thiophene ring. A general method for methylating 2-R-imidazoles with methyl iodide KOH-dimethoxy ethane is proposed.

2-Substituted imidazoles. 1. Reactions of 1-methyl-2-(2-furyl)imidazole with electrophiles

Abstract1-Methyl-2-(2-furyl)imidazole has been synthesized. Electrophilic attack (bromination, nitration, formylation, acylation, and hydroxymethylation) occurs in most cases at the free α-position of the furan ring.

Research on the chemistry of 2-hetarylbenzimidazoles. 5. Acylation of 1-methyl-2-(2′-hetaryl)benzimidazoles

The acylation of 1-methyl-2-(2′-furyl)- and 1-methyl-2-(2′-thienyl)benzimidazoles was studied. A convenient method for the formylation of the furan and thiophene rings by the action of urotropin in polyphosphoric acid (PPA) was found. Acylation of the furan and thiophene rings was realized by the action of acetic acid and aromatic carboxylic acids in PPA.

Chemistry of 2-hetarylbenzimidazoles. 8. Synthesis and properties of 1-methyl-2-(5′-methyl-2′-selenienyl)benzimidazole

Abstract1-Methyl-2-(5′-methyl-2′-selenienyl)benzimidazole was synthesized and subjected to electrophilic-substitution reactions: nitration, bromination, sulfonation, chloromethylation, formylation, and acylation. The substituent usually enters the 4′ position of the selenophene ring, but nitration with acetyl nitrate leads to a mixture of 5′-nitro and 4′-nitro derivatives. Oxidation of 2-selenienylbenzimidazole with potassium permanganate leads to the 5′-carboxy derivative, while oxidation with selenium dioxide leads to the 5′-hydroxymethyl and 5′-formyl derivatives.

Chemistry of 2-hetarylbenimidazoles. 7. Transformations of trans-1-methyl-2-[Β-(2′-furyl)vinyl] benzimidazole

Electrophilic substitution reactions in the furylvinylbenzimidazole series were studied. In nitration, sulfonation, bromination, acylation, formylation, and hydroxymethylation reactions, the substituent enters at the α-position of the furan ring. The presence of a vinylene group reduces the influence of the benzimidazole fragment on the furan ring, and therefore the reactions in the latter proceed considerably more rapidly and under milder conditions than in the case of furylbenzimidazole. Calculated data are given for the π-electronic density on the carbon atoms of furyl-vinylbenzimidazole, obtained by the CNDO method.

Research on the chemistry of 2-hetarylbenzimidazoles

The condensation of 1-methyl-2-formylpyrrole with o-phenylenediamine gave 2-(1′-methyl-2′-pyrrolyl)benzimidazole, which was subjected to methylation. The alkylation product was subjected to electrophilic substitution. The substituent is incorporated in the 4 or 5 position of the hetaryl ring; however, bromination of 1-methyl-2-(1′-methyl-2′-pyrrolyl)benzimidazole leads to the formation of the mono-, di-, and tribromo derivatives, depending on the conditions. The acidophobic properties of the pyrrole ring are partially lost as a consequence of the effect of the benzimidazole ring.

2-Substituted imidazoles. 3. Metallation of 1-methyl-2-phenyl- and 1-methyl-2-(furyl-2)imidazoles

Abstract1-Methyl-2-phenylimidazole reacts with butyllithium to give 5-lithium substituted products. On the other hand, 1-methyl-2-(furyl-2)imidazole is metallated under the same conditions exclusively on the furan ring and primarily in the 3 position. The introduction of triethylamine into the reaction mixture, or replacement of butyllithium by lithium 2,2,6,6-tetramethylpiperidide leads to the formation of a lithium derivative substituted at the 5-position of the furan ring exclusively.

Investigations in the field of the chemistry of 2-hetarylbenzimidazoles. 6. Synthesis and properties of 1-methyl-2-(2′-selenienyl)benzimidazole

Abstract2-(2′-Selenienyl)benzimidazole has been synthesized by a Weidenhagen reaction and converted into the N-methylated derivative. Electrophilic-substitution reactions (nitration, sulfonation, bromination, chloromethylation, and acylation) in the selenophene ring have been studied. It has been shown that the substituent enters the α position of the selenophene ring in most cases. The bromination of 1-methyl-2-(2′-selenienyl)benzimidazole in acetic acid produces the 3′,5′-dibromo derivative, whereas 1-methyl-5(or 6)-bromo-2-(3′,5′-dibromo-2′-selenienyl)benzimidazole is obtained in polyphosphoric acid.

Research on the chemistry of 2-hetarylbenzimidazoles. 4. Oxidation of 1-methyl-2-(5′-methyl-2′-hetaryl)benzimidazoles

The methyl group in 1-methyl-2-(5′-methyl-2′-hetaryl)benzimidazoles (hetaryl = furyl and thienyl) was oxidized. It was found that a salt of a carboxylic acid, which in an acidic medium loses carbon dioxide to give 1-methyl-2-(2′-furyl)-benzimidazole, is formed when 1-methy1-2-(5′-methyl-2′-furyl)benzimidazole is treated with an aqueous solution of potassium permanganate. The carboxy derivative of thiophene is considerably more stable. Oxidation by means of selenium dioxide leads to the corresponding 5′-formyl derivative. The structures of the compounds obtained were confirmed by data from the IR and PMR spectra.

Research on the chemistry of 2-hetarylbenzimidazole. 3. Reaction of 1-methyl-2-(5?-methyl-2?-hetaryl) benzimidazoles with electrophilic reagents

A number of new derivatives of 1-methyl-2-(5′-methyl-2′-hetaryl)benzimidazole were synthesized by electrophilic substitution. The substituent enters the β position of the 4′-hetaryl ring. A furan ring that contains a methyl group in the 5′ position undergoes profound destructive oxidation under the influence of acetyl nitrate. Depending on the conditions, bromination leads to the formation of bromo derivatives that are substituted in the benzene or hetaryl ring.