Pyrroles from ketoximes and acetylene. 35. Synthesis of 2-(4-alkylthiophenyl)pyrroles and their 1-vinyl derivatives

2-(4-Alkylthiophenyl)- and 2-(4-phenylthiophenyl)pyrroles and their 1-vinyl derivatives were synthesized by the reaction of 4-alkylthio- and 4-phenyl-thioacetophenone oximes with vinyl chloride in a KOH-DMSO system at 120 and 130C and at atmospheric pressure.See [1] for Communication 34.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1486–1488, November, 1987.     

Pyrroles from ketoximes and acetylene. 41. Some reactions of 1-vinyl-2-(2-furyl)- and-(2-thienyl)pyrroles

We have studied the reaction of 1-vinyl-2-(2-furyl)- and -(2-thienyl)pyrroles with trifluoroacetic anhydride, with hydrogen in the presence of catalysts (Raney nickel, palladium black, palladous chloride), with propargyl alcohol in electrophilic conditions [catalysis by perfluorobutyric acid in the system azoisobutyrodinitrile (AIBN)-CCl₄), and with alkane thiols with AIBN initiation. The products are novel substituted hetarylpyrroles.See [1] for Communication 40.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 337–342, March, 1991.     

Pyrroles from ketoximes and acetylene.

2-Aryl- and 1-viny1-2-pyrroles were synthesized by condensation of p-substituted acetophenone oximes with acetylene under pressure in superalkaline media (KOH/DMSO). The initially formed nitrogen-unsubstituted pyrroles can be vinylated in the presence of acetylene. Lithium hydroxide, which is completely inactive in the vinylation step, was found to be a selective catalyst for the construction of a pyrrole ring from oximes of aliphatic aromatic ketones. In the case of aliphatic and cycloaliphatic ketoximes (for example, cyclohexanone oxime) LiOH has virtually no catalytic effect on the reaction. The yields of 1-viny1-2-ary1-pyrroles depend substantially on the substituent in the phenyl ring. The structures of the synthesized compounds were confirmed by the IR, PMR, UV, and ¹³C NMR spectra.See [1] for communication II.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 489–491, April, 1978.     

Pyrroles from ketoximes and acetylene

The reaction between ketoximes CH₃(RCH₂)C = NOH and acetylene in the presence of KOH and dimethyl sulfoxide at 120°C leads exclusively to 1-vinyl-2-methyl-3-R-pyrroles in 73–87% yields. The regiospecificity of the reaction is disrupted when the temperature is raised, and the fraction of a second isomer (1-vinyl-2-RCH₂-pyrrole) reaches 20–50% at 140°C. Regioselectivity is not observed for R¹CH₂(R²CH₂)C = NOH (R¹ and R² = n-alkyl). The relative shifts of the signals of the ring protons and the vinyl group for a number of 2-alkyl-1-vinyl- and 2,3-dialkyl-1-vinylpyrroles were measured. Alkyl substituents have a distinct effect on the chemical shifts of the protons of the 4–5 bonds. As the volume of the 2-alkyl substituent increases the protons of the N-vinyl group are deshielded by 0.10–0.13 ppm, and the 4-H ring proton is shielded by 0.05–0.16 ppm; this is explained by steric inhibition of the p- conjugation in the N-vinyl group during an s-trans(anti)-gauche conformational transition.This is actually communication XVI. The first publications (for example, see [1–3] and the literature cited in them) were not numbered.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 54–59, January, 1978.     

Pyrroles from ketoximes and acetylene

On the basis of a comparative study and analysis of the chemical shifts in the ¹³C NMR spectra of 1-vinyl-2-arylpyrroles and 3-alkyl-1-vinyl-2-phenylpyrroles, as well as 2-phenyl- and 1-ethyl-2-phenylpyrroles, it was established that the effects of substituents in the investigated series are transmitted via a mechanism involving conjugation and induction; the conductivity and polarizability of the 2-arylpyrrole system increase when a vinyl group is introduced in the 1 position or, in the case of the 1-vinylpyrrole system, when a phenyl group is introduced in the 2 position; this is due to the increase in the degree of overall conjugation.See [1] for communication IV.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 768–772, June, 1978.     

Pyrroles from ketoximes and acetylene 8. Synthesis of 4,5,6,7-tetrahydroindole and its 1-vinyl derivative

4,5,6,7-Tetrahydroindole or 1-vinyl-4,5,6,7-tetrahydroindole was obtained in 81 and 93% yields, respectively, by reaction of cyclohexanone oxime with acetylene at 90–140C in the presence of alkali metal hydroxides or alkoxides in dimethyl sulfoxide (DMSO) or mixtures of DMSO with low-polarity or nonpolar solvents. The reaction is effective both in an autoclave (initial pressure 8–16 gage atm) and at atmospheric pressure.See [1] for communication 7.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 197–199, February, 1979.     

Pyrroles from ketoximes and acetylene

The ¹³C NMR spectra of eight 2-alkyl- and 2,3-dialkyl-1-vinylpyrroles were studied. The ¹³C chemical shifts of all of the carbon atoms of the ring and the vinyl group depend substantially on the position and structure of the alkyl substituent. As the branched character of the alkyl group in the 2 position increases, the signal of the -carbon atom of the vinyl group is shifted to weak field due to weakening of the p- conjugation in the N-vinyl group because of disruption of its coplanarity with the pyrrole ring. The conjugation between the double bond and the pyrrole system involves competition for possession of the p electrons of the nitrogen atom.See [16] for communication II.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 350–354, March, 1978.     

Pyrroles from ketoximes and acetylene

2-(2-Furyl)pyrroles and 1-vinyl-2-(2-furyl)pyrroles were obtained in up to 80% yields in the reaction of ketoximes of the furan series with acetylene in MOH—dimethyl sulfoxide (M = Li, K) Superbase media.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1058–1061, August, 1981.     

Pyrroles from ketoximes and acetylene

The respective 2-aryl- and N-vinyl-2-arylpyrroles were obtained by the reaction of the oximes of alkyl aryl ketones with acetylene in the superbasic medium MOH (M=Li, K)-DMSO. Their yields depended largely on the structure of the ketoximes and on the reaction conditions.For Communication 41, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 609–613, May, 1992.     

Pyrroles from ketoximes and acetylene

A series of previously unknown trifluoroacetyl derivatives of pyrroles were obtained with high yields by the reaction of pyrroles, including N-vinyl-substituted pyrroles, with trifluoroacetic anhydride in the presence of pyridine at room temperature. The solvent and the substituents at the and positions of the pyrrole ring do not affect the direction of electrophilic substitution.For Communication 37, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 48–52, January, 1989.     

Pyrroles from ketoximes and acetylene. 43. 1,2-Dihaloalkanes and vinyl chloride in the synthesis of 2-(4-alkylthiophenyl)pyrroles

2-(4-Alkylthiophenyl)-3- and 2-(4-alkylthiophenyl)-5-methylpyrroles and their 1-vinyl derivatives were synthesized by the reaction of alkyl(4-alkylthiophenyl)ketoximes with dihaloalkanes or vinyl chloride in the KOH-DMSO system at 120–140C and atmospheric pressure.See [1] for Communication 42.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1, 1337–1340, October, 1990.     

Pyrroles from ketoximes and acetylene. 46. Pyrroles with sterically hindered substituents

The corresponding pyrroles and their N-vinyl derivatives were obtained by the catalyzed (by an MOH-DMSO superbase) reaction of acetylene and its crypto forms (vinyl chloride, 1,2-dichloroethane) with alkyl-2,4-, alkyl-2,5-, and alkyl-3,4-dimethylphenylketoximes. Reaction intermediates — O-vinylketoximes — were detected.For Communication 45 See [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1320–1323, October, 1991.     

Pyrroles from ketoximes and acetylene. 44. Methyl aryl ketoximes with reactive substituents

The Trofimov reaction was extended to methyl aryl ketoximes with substituents in the benzene ring that are unstable with respect to the action of a strongly basic medium. The corresponding pyrroles and their 1-vinyl derivatives were obtained. 4-Nitroacetophenone oxime, from which only 2-phenyl- and 1-vinyl-2-phenylpyrrole were obtained, and 4-bromoacetophenone oxime, the reaction of which leads to the formation of 1-vinyl-2-(4-vinyloxyphenyl)pyrrole in addition to the principal 2-(4-bromophenyl)pyrrole, constituted exceptions.For communication 43, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 187–191, February, 1991.     

Pyrroles from ketoximes and acetylene. 24. Acidic hydrolysis of 1-vinylpyrroles

The hydrolysis of 2-methyl-, 2-phenyl-, and 3-methyl-2-phenyl-1-vinylpyrroles and 1-vinyl-4,5,6, 7-tetrahydroindole in the presence of HCl, H₂SO₄, NH₂OH-HCl, acetic acid, and H₂O₂ in aqueous, aqueous dioxane, and aqueous alcohol solutions leads to oligomers with complex structures and compositions, viz., products of acidic catalytic and oxidative condensation of the starting compounds and the resulting pyrroles both with one another and with the liberated acetaldehyde. 2-Phenylpyrrole was obtained in 52% yield from 1-vinyl-2-phenylpyrrole by hydrolysis in a dilute (0.5%) solution [water-dioxane (59)] with excess NH₂OH.HCl, which ties up the acetaldehyde.See [1] for Communication 23.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1631–1639, December, 1982.     

Pyrroles from ketoximes and acetylene. 19. Regioselectivity of the reaction of alkyl benzyl ketoximes with acetylene

Alkyl benzyl ketoximes react with acetylene at 60–150 °C in MOH-dimethyl sulfoxide (M = Li, K) primarily by means of the methylene group of the benzyl grouping, which is primarily anti-oriented with respect to the hydroxy group, to give 2-alkyl-3-phenylpyrroles in greater than 70% yields. The specific participation of the antimethylene group in the construction of a pyrrole ring constitutes evidence against mechanisms that include a [3,3]-sigmatropic shift in O-vinyl oximes. It follows from the results obtained that the reaction proceeds through an anti-dianion of the benzyl type stabilized by conjugation with the aromatic ring.See [1] for communication 18.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 193–198, February, 1982.     

Pyrroles from ketoximes and acetylene. 11. Conformation of 1-vinylpyrroles from1H NMR data

A number of 1-vinylpyrroles were studied by PMR spectroscopy. Bulky substituents in the position of the pyrrole ring give rise to deshielding of h_b and a decrease in²J(H_A,H_B) and⁶J(H₃,H_B). The results were interpreted as a decrease in the p, conjugation in the N-vinyl group due to distortion of the coplanarity. The dihedral angle () between the planes of the pyrrole ring and the double bond was estimated (with an accuracy of ±5 °).See [10] for our previous communication [10].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 328–330, March, 1980     

Pyrroles from ketoximes and acetylene. 30. The synthesis of 3-alkyl-2-arylpyrroles

Conditions were found for the synthesis of 3-alkyl-2-arylpyrroles using the Trofimov reaction at 50–70 °C both at elevated and atmospheric pressure. O-Vinyloximes and 3H-5-hydroxy-4,5-dihydropyrroles were isolated as intermediates.Communication 29, see ref. [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1501–1505, November, 1985.     

Pyrroles from ketoximes and acetylene. 14. Quantitative estimate of the effect of substituents on the NH acidities of pyrroles

The pK values of a series of substituted pyrroles and the vNH values (in dimethylformamide), which characterize their relative acidities were measured by the transmetallation method. It was established that the acidities of pyrroles are determined primarily by the inductive effect of the substituents and are virtually independent of the ability of the latter to enter into conjugation with the ring. This means that the electron pair of the anion that is set free in the ionization of pyrrole retains character. The linear dependences of the pK and NH values on the inductive constants (I) of the substituents can be used to estimate the pK values of various compounds that contain a pyrrole ring starting from the NH and I values.See [1] for communication 13.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 632–638, May, 1980.     

Pyrroles from ketoximes and acetylene. 45. A new route to 2,2-dipyrroles

The reaction of 1-methyl-2-acetylpyrrole oxime with acetylene at atmospheric and increased pressure can be catalyzed by KOH-DMSO superbase to give 1-methyl-2-(2-pyrrolyl)pyrrole, N-vinyl-2-[1-methyl(2-pyrrolyl)]pyrrole, and the reaction intermediate methyl-2-(1-methylpyrrolyl)-O-vinyloxime.See [1] for Communication 44.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 460–463, April, 1991.     

Pyrroles from ketoximes and acetylene. 40. Reaction of alkyl hetaryl ketoximes with 1,2-dichloroethane in superbase media

2-(2-Furyl)- and 2-(2-thienyl)pyrroles and their N-vinyl derivatives were synthesized by the reaction of alkyl furyl (thienyl) ketoximes with 1,2-dichloroethane in superbase media. 2-Chloroethyl and vinyl ethers of alkyl hetaryl ketoximes are intermediates in the reaction.See [1] for Communication 39.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 901–906, July, 1989.