Protonation of pyrrolo [1,2-α] Pyrimidine derivatives

The protonation of pyrrolo [1,2-] pyrimidine and 6, 7, 8, 9-tetrahydropyrimido [1, 2-] indole derivatives in CF₃COOH (at –15 to +25° C) and in CF₃COOH/H₂SO₄ (at 25°) was studied by PMR spectroscopy. The investigated compounds form monocations, the structure of which corresponds to the addition of a proton to the carbon atom of th pyrrole fragment in the position to the bridge nitrogen atom.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 686–692, May, 1976.     

Synthesis and ionization constants of N-(4-carbethoxy-5-pyrazolyl)amidines

A number of N-(4-carbethoxy-5-pyrazolyl) amidines were synthesized by the reaction of acetals of amides and lactams with 4-carbethoxy-5-aminopyrazole, and their ionization constants in 50% alcohol were measured. It is shown that the increased basicities of the amidines obtained from the lactam acetals and dimethylacetamide acetal as compared with the basicity of N-(4-carbethoxy-5-pyrazolyl)-N,N-dimethylformamidine are due to the smaller degree of steric hindrance to conjugation in the latter.Communication XXIV from the series Acetals of lactams and acid amides. See [1] for communication XXIII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 379–381, March, 1978.     

Acetals of lactams and acid amides. 48. Reaction of enamino diketones with amide crystals. Synthesis of derivatives of coumarin and carbostyril

It was established that the reaction of derivatives of 2-aminomethylenecyclohexane-1,3-dione with N,N-dimethyl-diethylacetal gives dienediamines, heating of which in aqueous hydrochloric acid leads, depending on the structure, to derivatives of carbostyril and/or coumarin. This unusual reaction is based on initial attack at the position of the enamino diketone by the ketone acetal, which exists in equilibrium with the starting amide acetal.See [1] for Communication 47.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1470–1476, November, 1987.     

Lactam acetals and acid amides. 31. Synthesis,protonation, and basicities of some heterocyclic enamino ketones

The protonation of cyclic enamino ketones of the pyrrolidine, piperidine, and hexahydroazepine series, as well as their noncyclic analogs, was studied by PMR spectroscopy. It is shown that the presence of a CH₂ or CH₃ group in the “enamine” position leads to C protonation (in CF₃COOH). In the case of enamino ketones that do not contain substituents in the “enamine” α position N-and O-protonated forms are observed in CF₃COOH. The measured pK_a values (in 10% alcohol) and the ΔpK_a values (in nitromethane) of the enamino ketones show that the compounds for which C protonation is characteristic are two to three orders of magnitude more basic than in the case of compounds that do not contain substituents in the “enamine” α position; this is explained by the different character of protonation. See [1] for communication 30. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 344–348, March, 1980     

sym-Triazine derivatives

The structures, tautomerism, and acid-base properties of some sym-triazinyl-substituted CH acids were studied.See [1] for Communication 6.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 241–249, February, 1988.     

Indole derivatives. 131. The basicity of 5- and 6-aminoindoles

The pK_a values for the 5- and 6-aminoindoles were determined from potentiometric titration curves and from ¹³C NMR data on the total change of the chemical shifts of the carbon atom signals on protonation of the amino group. The pK_a values obtained (5.99 and 5.53) were higher than those of aniline (3.92) or -naphthylamine (3.39).For Communication 130, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, 766–769, June, 1988.     

Protonation of 1, 5-naphthyridine derivatives

The direction of protonation (1-N or 5-N) or 2-, 2,3-, and 2,6-substituted derivatives of 1,5-naphthyridine was determined on the basis of the basicity constants.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 965–968, July, 1977.     

Protonation of pyrrolo[1,2-a]benzimidazole derivatives

The protonation of a number of pyrrolo[1,2-a]benzimidazole derivatives in trifluoroacetic acid was studied by PMR spectroscopy. 1,3-Unsubstituted compounds are protonated exclusively at the C₁ atom. Under similar conditions, pyrrolobenzimidazoles that have a methyl group in the 1 position form a mixture of two protonated forms, which correspond to the addition of a proton to C₁ and C₃, respectively. The relative percentage of the C₃-protonated form decreases successively (from 81 to 18%) on passing from the 3-unsubstituted compound to the corresponding 3-phenyl and 3-methyl derivatives. The basicity constants of the pyrrolobenzimidazoles decrease symbatically with an increase in the relative percentage of this form. The relative proton-acceptor capacity of indolicine, pyrrolo[1,2-a]-imidazole, and pyrrolo[1,2-a]benzimidazole were examined on the basis of the protonation data and the reactivity indexes, calculated by the simple Hückel MO method.Translated from Khimiya Geterotsiklicheskih Soedinenii, No. 8, pp. 1132–1137, August, 1972.     

Synthesis and ionization constants of 2-aryliminotetrahydrofurans

The tetrafluoroborates of 2-aryliminotetrahydrofurans were synthesized by the reaction of 0-ethylbutyrolactonium tetrafluoroborate with aromatic amines, and a number of bases of imido esters with various substituents in the aromatic ring were synthesized by the reaction of aromatic amines with 2,2-diethoxytetrahydrofuran. The ionization constants of the products were measured. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 737–740, June, 1980.