L. V. Baikalova

Assembling of Complex Heterocyclic Ensembles, Schiff Bases, from 5-Amino-3-[2-(4,5,6,7-tetrahydroindolyl)]pyrazoles and 1-Vinyl(ethyl)-2-formylimidazoles

Condensation of 5-amino-3-(2-pyrrolyl)pyrazoles with 1-vinyl(ethyl)-2-formylimidazoles afforded complex heterocyclic ensembles: Schiff bases containing pyrrole, pyrazole, and imidazole rings. The cis,trans-orientation of CH = N and CH2 = CH groups and E-isomeric structure of the Schiff bases under study with respect to the imine fragment, and also the presence of intra- and intermolecular hydrogen bonds were established.

The study of benzimidazoles

The nature of the first two long-wave bands in the UV spectra of 2-substituted benzimidazoles has been analyzed on the basis of photoelectron spectra (PES). Three basic types of spectroscopic situations are typical of these compounds: 1) a change in the sequence of the occupied MO of the ground state does not influence the order of the excited energy levels; 2) when the π-levels are in the same order, inversion of the excited states occurs; 3) reversal of the occupied π-MO of the ground state causes the inversion of the excited states.

Reaction of Tribenzylphosphine Oxide with Aldehydes

Tribenzylphosphine oxide readily and stereoselectively reacts with aliphatic, aromatic, and heteroaromatic aldehydes in the presence of strong bases yielding exclusively (or predominantly) E-isomers of 1-organyl-2-phenylethenes and dibenzylphosphinic acid.

Synthesis and structure of azomethines based onN-vinyl derivatives of 2-amino- and 2-formylimidazoles

New Schiffs bases of theN-vinylimidazole andN-vinylbenzimidazole series were synthesized.1H NMR data suggest that the azomethines exist in theE-form with respect to the CH=N bond and that the vinyl groups havetrans-orientation relative to each other.

Specific intramolecular C-H...O interactions in 1-vinyl-2-formylimidazole and 1-vinyl-2-formylbenzimidazole studied by1H and13C NMR spectral data

According to the1H and13C NMR spectral data, the vinyl group in 1-vinyl-2-formylimidazole and 1-vinyl-2-formylbenzimidazole istrans-oriented with respect to the formyl fragment, while the carbonyl group occupies theanti-position with respect to the N atom of pyridine cycle. A specific intramolecular C—H...O interaction of a weak hydrogen bond type is realized between the α-H atom of the vinyl group and O atom of the carbonyl group.

Intramolecular specific C-H... N interactions with participation of the pyridine ring nitrogen atom and amino and imino groups in 2-substituted 1-vinylbenzimidazoles, according to1H and13C NMR data

In 1-viny1–2,2′-pyridylbenzimidazole, a double intramolecular specific C-H...N interaction is accomplished between the α-H of the vinyl group with the pyridine ring nitrogen and between the H3′ atom of the pyridine ring and the benzimidazole ring nitrogen. In 1-viny1–2-aminobenzimidazole, there are no intramolecular interactions between the hydrogen atoms of the vinyl group and the nitrogen of the amino group. In 1,3-divinyl-2-iminobenzimidazole, the specific interaction of the imino group nitrogen with the β-cis-hydrogen of the vinyl group is greatly weakened by a degenerate tautomeric equilibrium.

Condensation reactions of vinyl and ethyl derivatives of 2-amino-and 2-formylimidazoles

New Schiff bases of 1-vinyl- and 1-ethyl-substituted imidazoles and benzimidazoles were synthesized. The condensation reactions of 2-amino- and 2-formylimidazoles with 2-aminobenzimidazoles are virtually independent of the nature of the substituent (CH=CH2 or Et) at position 1 of the heterocycle. The structures of the azomethines synthesized were established by1H NMR and IR spectroscopy.

Synthesis ofN-allenylazoles from azoles and propargyl chloride or 1,2,3-trichloropropane in one preparative step

Reactions of imidazole and 1,2,4-triazole with propargyl chloride and its more accessible equivalent, 1,2,3-trichloropropane, in the superbasic KOH-DMSO system have been studied. The reactions afford the correspondingN-allenylazoles in one preparative step.

Basicity of azoles

According to the data of photoelectron spectroscopy, a linear dependence exists between the energies of nonbonding electrons in azoles and azines, on the one hand, and their benzoannelated derivatives, on the other hand. Substituents do not disturb this relationship; those in position 2 of N-heterocycles exert effects of the same type on the ionization potentials of the n-level of 1,3-diazole and pyridine.

Reaction of 2-aminobenzimidazole with acetylene

The reaction of 2-aminobenzimidazole (1) with acetylene under pressure proceeds with the formation of vinyl monomers, corresponding to amine and imine forms, 1-vinyl-2-amino- and 1,3-divinyl-2-iminobenzimidazoles, depending on the reaction conditions. 1,3-Divinyl-2-benzimidazolone was also isolated in aqueous dioxane in addition to the monovinyl derivative of1. Cyclization of the divinyl derivative of1 with acetylene proceeds to give 9-vinyl-1,2-dimethylimidazo[1,2-a]-benzimidazole.