A general method for the catalytic nazarov cyclization of heteroaromatic compounds

A general, catalytic method for efficient Nazarov cyclization of systems containing heteroaromatic components has been developed. Scandium triflate was identified as the most reactive promoter, and it was found that addition of lithium perchlorate was necessary for synthetically useful catalytic cyclizations. The method was used to synthesize a range of cyclopentanone-fused heteroaromatic systems in 36-97% yield, and the reactivity trends observed demonstrate the impact of polarization on cyclization efficiency. [reaction: see text].     

Quantum-chemical calculations of the spectroscopic parameters of heteroaromatic compounds containing sulfur and selenium atoms

Conclusions A new single set of spectroscopic parameters of the CNDO method for compounds containing sulfur and selenium atoms, which permits the simultaneous calculation of the ionization potentials and energies of the electronic transitions on a semiquantitative level, has been proposed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2251–2253, October, 1986.     

Olefin cross-metathesis for the synthesis of heteroaromatic compounds

The olefin metathesis reaction has underpinned spectacular achievements in organic synthesis in recent years. Arguably, metathesis has now become the foremost choice for a carbon-carbon double bond disconnection. Despite this general utility, de novo routes to heteroaromatic compounds using the cross-metathesis (CM) reaction have only recently emerged as an efficient strategy. This approach allows a convergent union of simple, functionalised, three- to four-carbon olefinic core building blocks, to generate furans, pyrroles and pyridines with a high degree of control of substitution pattern in the product.     

Relative reactivities of heteroaromatic cations towards reduction by 1,4-dihydronicotinamides

Kinetic data are reported for the equilibration of the 1-methyl-3-nitropyridinium cation with its pseudobase (hydroxide adduct) and for the reduction of this cation by 1-benzyl-1, 4-dihydronicotinamide. The C-2 hydroxide adduct is the kinetically controlled product (pK_R+ = 11.6) when this pyridinium cation is mixed with aqueous base, however, this species rearranges to the C-4 adduct as the themodynamically more stable product (pK_R+ = 9.42). The pH-dependence of this equilibration may be analysed to give k_OH = 1600 M^-1s^-1 for hydroxide ion attack at C-4 of this cation. Reduction of this pyridinium cation by 1-benzyl-1, 4-dihydronicotinamide appears to occur exclusively at C-4 with second-order rate constant k₂ = 0.72 M^-1s^-1 and k₂ ^H/k₂^D = 2.0 in 20% CH₃CN - 80% H₂O, ionic strength 1.0, 25°C.The reactivities of pyridinium, quinolinium, isoquinolinium, acridinium and phenanthridinium cations of pK_R+ = 10.0 towards both hydroxide ion and 1-benzyl-1, 4-dihydronicotinamide are evaluated. Relative reactivities (K₂/K_OH) for these two processes are shown to be acridinium : quinolinium (C-4) : pyridinium (C-4) : quinolinium (C-2) : isoquinolinium : phenanthridinium = 1.6×10⁵ : 3400 : 80 : (4 : 1.0 : 0.7 for predominantly aqueous reaction media. These data support the hypothesis that formation of 1, 2-dihydropyridine systems upon reduction of heteroaromatic cations by 1, 4-dihydronicotinamides occurs via direct one step hydride transfer, while formation of 1,4-dihydro-pyridines in such processes occurs preferentially by a mechanistica11y more complex process involving electron transfer.     

Model calculations for reactivities of polycyclic aromatic hydrocarbon metabolites

Structure-resonance theory calculations correlate reactivities and mutagenicities of polycylic aromatic hydrocarbon metabolites.     

New unsymmetrical difluoroaromatic compounds and estimation of their reactivities in nucleophilic substitution

A series of previously unknown unsymmetrical difluoroaromatic compounds, viz., p-fluorobenzoylphenyl(p-fluorophenyl)-substituted imidazoles, pyrazines, and quinoxalines, were synthesized according to multistep procedures with the use of chloral as the key compound. The reactivities of the resulting difluoroaromatic compounds were estimated based on ¹⁹F and ¹³C NMR spectral data and the results of quantum-chemical calculations. The calculated charge densities on the C_ipso atoms correlate linearly with the experimental chemical shifts in the ¹⁹F and ¹³C NMR spectra. Difluoroaromatic compounds, which are characterized by _F > –110 and _C > 163 and by the charge density on the C_ipso atom higher than 0.08 e, are sufficiently activated to be used for the preparation of high-molecular-weight polyethers.     

Electrophilic activation of acetyl-substituted heteroaromatic compounds

The chemistry of acetyl-substituted pyridines, thiazoles, quinoline, isoquinolines, and pyrazine (1-9 and 28) has been studied. These heteroarenes (1-8) condense with benzene in good yields (74-96%) in the Bronsted superacid, CF(3)SO(3)H (triflic acid). In these acid-catalyzed hydroxyalkylation reactions, compounds 1-8 are significantly more reactive than acetophenone. It is proposed that compounds 1-8 readily form dicationic electrophiles in triflic acid.     

New method for the synthesis of macrocyclic compounds

A mixture of isomers corresponding to closing of the ring at the 3 and 4 positions of the thiophene ring is formed during intramolecular acylation of 12-(5-methyl-2-thienyl)-lauryl chloride in a homogeneous medium; the reaction proceeds primarily to favor the formation of the isomer with the larger ring (80%). A method for the synthesis of macrocyclic -alkylcycloalkanones by reductive desulfurization of the corresponding bicyclic ketones, which contain thiophene rings, was developed.See Izv. Akad. Nauk SSSR, Ser. Khim., 2228 (1970) for Communication XI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1467–1472, November, 1970.     

New method for the synthesis of macrocyclic compounds

The intramolecular acylation of acid chlorides of ω-thienylalkanoic acids of various structures in the presence and absence of silica gel was investigated. The reaction of aluminum chloride etherate and the indicated acid chlorides with the surface groups of silica gel was studied by IR spectroscopy, and the role of the compounds formed on the surface in the reaction under consideration was discussed. A sequence of processes and a mechanism involving participation of the solid phase in the intramolecular acylation of acid chlorides of ω-thienylalkanoic acids are formulated.     

New method for the synthesis of macrocyclic compounds

The intramolecular acylation of acid chlorides of -(3-methyl-2-thienyl)- and -(4-methyl-2-thienyl)alkanoic acids proceeds at the free 5 position of the thiophene ring. A solid-phase effect (silica gel), which, under comparable conditions, leads to more than double the yields, is displayed during the cyclization of acid chlorides of the above acids. A modification was developed for the reductive desulfurization of cyclothienones with alkyl groups in the position of the thiophene ring; the modification includes the formation of unsaturated compounds and products of the reduction of the carbonyl group. A new route to the synthesis of - and -methylcycloalkanones, including DL-muscone, was developed.See [2] for communication XIII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 170–176, February, 1972.     

New method for the synthesis of macrocyclic compounds

A method was developed for the preparation of macrocyclic 2-alkylcycloalkanones by alkylation of 2-carbethoxy--cyclothienones with subsequent desulfurization and ketone cleavage. Only C-alkylation occurs under the described conditions (potassium metal in hexamethylphosphoric triamide, sodium hydride in dioxane).See [1] for communication XIV.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 16–21, January, 1973.     

New method for the synthesis of macrocyclic compounds

Summary On the basis of transformations carried out witht [10]--cyclothien-1-one it is shown that the higher substituted cycloaliphatic compounds can be prepared from bicyclic compounds containing a thiophene nucleus.Ultraviolet spectra were determined in alcoholic solution with a Hitati (japan) recording spectrophotometer by V. A. Petukhov, whom the authors thank. The Chromatographie analyses were carried out on the Chromatograph designed by the Special Design Office of the Institute of Organic Chemistry by V. I. Yakerson, whom we thank.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya No. 11, pp. 2055–2060, November, 1964     

New method for the synthesis of macrocyclic compounds

Conclusions Results are given which confirm the influence of silica gel on the selectivity of the intramolecular reaction.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 572–576, March, 1968.     

Palladium-catalyzed reductive N-heterocyclization of alkenyl-substituted nitroarenes as a viable method for the preparation of bicyclic pyrrolo-fused heteroaromatic compounds

Palladium-catalyzed, carbon monoxide-mediated reductive N-heterocyclization of nitro-heteroaromatic compounds having an alkene adjacent to the nitro-group affords bicyclic pyrrolo-fused heteroaromatic molecules. This type of reaction was used to prepare the fused bicyclo[3.3.0] ring-system: thieno[3,2-b]pyrrole, thieno[2,3-b]pyrrole, furo[2,3-b]pyrrole, pyrrolo[3,2-d]thiazole, and pyrrolo[2,3-d]imidazole and the bicyclo[4.3.0] ring-systems: pyrrolo[3,2-b]pyridine, pyrrolo[2,3-b]pyridine, pyrrolo[3,2-c]pyridine, pyrrolo[2,3-c]pyridine, pyrrolo[3,2-c]pyridazine, and pyrrolo[3,2-d]pyrimidine in 32-94% yield.     

Quantum-chemical investigation of some oligomeric heteroaromatic compounds

Indigo and its dimer, trimer, dehydro, and leuco forms were investigated within the framework of the Pariser-Parr-Pople method. The electronic structures of the compounds in the ground and excited states and the effect of chain lengthening are discussed, and the UV absorption spectra are interpreted. Several characteristics of the chromaticity of the investigated compounds as representatives of vat dyes are examined. The estimated (from calculations) energetic favorability of the indigoid, dehydro, and leuco forms of indigo is used in discussing the observed and experimental ease of redox transformations of indigo.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 794–798, June, 1972.