A. T. Soldatenkov

Synthesis of N-substituted 1H-indeno[2,1-b]pyridines

It was established that N-phenacyl and p-nitrophenacyl bromides and N-methyl-1-azafluorenium iodide, as well as N-phenacyl-7-nitro-1-azafluorenium bromide, are converted to N-substituted 1H-indeno[2,1-b]pyridines rather than to the corresponding yilds or indenoindolizines upon treatment with bases under various conditions. All of the pseudoazulenes of this type were isolated in the form of crystalline black or dark-violet substances. In contrast to pseudoazulenes of the 1H-indeno[1,2-b]-and 2H-indeno[2,1-c]pyridine series, they are stable both in the solid state and in solutions. 1H-1-Methylindeno[2,1-b]pyridine forms a perchlorate and a picrate (retention of the pseudoazulene structure) but is converted to N-methyl-1-azafluorenium chloride by the action of hydrogen chloride. Spectral characteristics are presented for all of the compounds obtained.

Reaction of indolizines with elemental sulfur

The fusion of 3,8-diphenyl-, 1,2-diphenyl-, and 6-methyl-2,7-diphenyl-indolizines with sulfur results in the formation of bis(indolizin-3-yl) disulfides with the respective substituents. Bis(2,8-diphenylindolizin-3-yl) disulfide is reduced to the original indolizine, and its treatment with nitric acid gives 2,8-diphenyl-1, 3-dinitroindolizine. Bis(dibenzo[b,g]indolizin-11-yl) disulfide is obtained from dibenzo[b,g]indolizine. The formation of the disulfides is apparently a general region of indolizines without substituents at C3 or C1 of the pyrrole ring. The structures of the disulfides obtained have been confirmed by data from x-ray diffraction analysis and NMR spectroscopy.

Electrophilic substitution of 1-methylindeno-1H-[2,1-b]pyridine

It is shown that electrophilic substitution of 1-methylindeno-1H-[2,1-b]pyridine takes place at the C9 atom in the case of acylation (acetylation, benzoylation, and formylation), bromination, and nitration. Data from the 13C NMR spectrum of this pseudoazulene confirm sp2 hybridization of the C9 atom.

Preparation of α- and γ-(α-furyl)pyridines

Mixtures of isomeric alkyl-substituted (in the pyridine ring) α- and γ-(α-furyl)-pyridines were obtained in up to ∼40% yields by condensation of furfural and ammonia with several aliphatic ketones and aldehydes (at 370–380 °C with a cadmium calcium phosphate catalyst). The dependence of the yields and structures of the corresponding isomers on the structure of the starting carbonyl compound was examined. Data from the PMR and mass spectra were used to prove the structures of the pyridine bases obtained.