Lubov N. Sobenina

General Route to Symmetric and Asymmetric meso-CF3-3(5)-Aryl(hetaryl)- and 3,5-Diaryl(dihetaryl)-BODIPY Dyes

A general efficient route to hitherto inaccessible symmetric and asymmetric meso-CF(3)-BODIPY dyes has been developed. The key stages include the reduction of available 2-trifluoroacetylpyrroles to the corresponding alcohols which are further condensed with pyrroles. The method allows the BODIPY with 3(5)aryl(hetaryl) and 3,5-diaryl(hetaryl) substituents to be readily assembled. The BODIPY dyes synthesized fluoresce (Φ(f) = 0.56-1.00) in the 560-680 nm region.

Reaction of Pyrrole Anions with Carbon Disulfide. Synthesis of Pyrrole-3-carbodithioates

Abstract 2,5-Disubstituted pyrroles react with carbon disulfide in the system KOH–DMSO with selective formation of pyrrole-3-carbodithioate anions from which pyrrole-3-carbodithioates were prepared by ethylation in 36–61% yield. From 2-methyl-5-phenyl(2-furyl- or 2-thienyl)pyrroles only pyrrole-3-carbodithioates are formed, with no isomeric pyrrole-4-carbodithioates being present. The reaction direction depends on pyrrole ring substitution: unsubstituted pyrrole selectively forms pyrrole-1-carbodithioate, whereas 2-methyl-, 2,3- and 2,4-dimethylpyrroles give exclusively pyrrole-2-carbodithioates under the same conditions.

Pyrrole-2-dithiocarboxylates: Synthesis of 2-(1-Alkylthio-2-cyanoethenyl)pyrroles

Abstract 2-(1-Alkylthio-2-cyanoethenyl)pyrroles were synthesized in good to high yields by reaction of pyrrole-2-dithiocarboxylates with active methylene nitriles in a KOH-DMSO medium. The condensation of 4,5,6,7-tetrahydroindole with cyanoacetate also leads to 1-ethylthio-2-cyano-4,5,6,7-tetrahydrocyclohexa-[c]-3H-pyrrolizin-3-one in 61% yield. The effect of substituent on the reaction course has been studied. The dipole moments and spectral characteristics of products are presented.

Stereoselective tandem ring opening of imidazoles with electron-deficient acetylenes and water: synthesis of functionalized (Z,Z)-1,4-diaza-2,5-dienes.

1-Substituted imidazoles undergo exceptionally facile stereoselective ring opening under the influence of electron-deficient acetylenes and water (equimolar ratio of the reactants) in MeCN at 45-60 °C without any catalysts to afford functionalized (Z,Z)-1,4-diaza-2,5-dienes, (Z,Z)-propenylaminoethenylformamides, in up to 80% yields. The reaction is rationalized to proceed in a tandem manner via zwitterionic vinyl carbanions formed by nucleophilic addition of imidazole to the triple bond. The carbanionic center is then quenched with water followed by the rearrangement of the intermediate 2-hydroxy-3-alkenylimidazolines.

Solvatochromism of Heteroaromatic Compounds: XVI. Theoretical Study of the Effect of Nonspecific Solvation on the Rotational Isomerism and Spectral Characteristics of 2-[2,2-Dicyano-1-(methylthio)vinyl]-5-methylpyrrole

The effect of nonspecific solvation of the relative stability of rotational isomers of 2-[2,2-dicyano-1-(methylthio)vinyl]-5-methylpyrrole was studied theoretically (HF/6-31G*) in terms of the Onsager model. In the free form this compound exists as an ensemble of four nonplanar C, N, S rotamers, the largest energy gap between which being no more than 2 kcal/mol. The effects of media whose generalized parameters correspond to chloroform and 1,2-dichlroethane reduce this gap to 0.7 and 0.5 kcal/mol. The vibration spectra of the rotamers and characteristics of the π→π* electronic transitions with intramolecular charge redistribution were calculated. Prospects of experimental studies of the solvatochromism and conformational isomerism of the title compound were discussed.

Solvatochromism of Heteroaromatic Compounds: XVII. Effect of Aprotic Inert Solvents on the Structure of 2-(2,2-Dicyanovinyl-1-methylthio)-5-methylpyrrole

The effect of aprotic inert media on the conformational structure of 2-(2,2-dicyanovinyl-1-methylthio)-5-methylpyrrole was studied by UV, NMR, and IR spectroscopy. Chloroform and less polar solvents stabilize only one of the four conformers. In more polar media, there is a dynamic equilibrium between all the possible conformers of the title compound. The state of the equilibrium depends both on the solvent and on the temperature.

Synthesis of 1-alkylthio-3H-indolizin-3-ones

We have recently tbund that 2-(t-alkylthio-2-cyanoethenyl)pyrroies are tbrmed in the reaction of ethyt pyrrole-2dithiocarboxylates of the I type with malonodinitrile and cyanoacetamide in the KOH--DMSO system with subsequent alkylation [1]. In attempting to extend this reaction to methylene-active compounds II with an ester grouping we observed that the principal (R = CH) or only pathway in this case is the formation of 1-ethylthio-3H-indolizin-3-ones IVa-c.

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.