Roman A. Irgashev

A new and convenient synthetic way to 2-substituted thieno[2,3-b]indoles

Summary A short and robust approach for the synthesis of 2-(hetero)aryl substituted thieno[2,3-b]indoles from easily available 1-alkylisatins and acetylated (hetero)arenes has been advanced. The two-step procedure includes the “aldol-crotonic” type of condensation of the starting materials, followed by treatment of the intermediate 3-(2-oxo-2-(hetero)arylethylidene)indolin-2-ones with Lawesson’s reagent. The latter process involves two sequential reactions, namely reduction of the C=C ethylidene double bond of the intermediate indolin-2-ones followed by the Paal–Knorr cyclization, thus affording tricyclic thieno[2,3-b]indoles.

A new synthetic approach to fused nine-ring systems of the indolo[3,2-b]carbazole family through double Pd-catalyzed intramolecular C–H arylation

A series of new polycyclic compounds bearing the 5,11-dihydroindolo[3,2-b]carbazole ring system, as the common motif of their nine-ring scaffolds, has been successfully prepared with the usage of an efficient two-step strategy, based on the double Friedel–Crafts acylation of 5,11-dihexyl-6,12-di(hetero)aryl-substituted 5,11-dihydroindolo[3,2-b]carbazoles with 2-iodobenzoyl chloride in the presence of SnCl4, followed by regioselective palladium-catalyzed cyclization of the obtained 2,8-bis(2-iodobenzoyl) derivatives into the desired fused 9H-fluoren-9-ones. Some modifications of these nine-ring structures have been performed to afford compounds of the same family bearing the 9H-fluorene fragments. Basic photophysical and electrochemical properties as well as thermal stability of the new fused indolo[3,2-b]carbazole derivatives have been determined.

Nitration of 5,11-dihydroindolo[3,2-b]carbazoles and synthetic applications of their nitro-substituted derivatives

A new general approach to double nitration of 6,12-di(hetero)aryl-substituted and 6,12-unsubstituted 5,11-dialkyl-5,11-dihydroindolo[3,2-b]carbazoles by acetyl nitrate has been developed to obtain their 2,8-dinitro and 6,12-dinitro derivatives, respectively. A formation of mono-nitro derivatives (at C-2 or C-6) from the same indolo[3,2-b]carbazoles has also been observed in several cases. Reduction of 2-nitro and 2,8-dinitro derivatives with zinc powder and hydrochloric acid has afforded 2-amino- and 2,8-diamino-substituted indolo[3,2-b]carbazoles, while reduction of 6,12-dinitro derivatives under similar reaction conditions has been accompanied by denitrohydrogenation of the latter compounds into 6,12-unsubstituted indolo[3,2-b]carbazoles. Formylation of 6,12-dinitro derivatives has proved to occur only at C-2, while bromination of these compounds has taken place at both C-2 and C-8 of indolo[3,2-b]carbazole scaffold. Moreover, 6,12-dinitro-substituted indolo[3,2-b]carbazoles have been modified by the reactions with S- and N-nucleophiles. Notably, the treatment of 6,12-dinitro compounds with potassium thiolates has resulted in the displacement of both nitro groups, unlike potassium salts of indole or carbazole, which have caused substitution of only one nitro group.

Synthesis of 4-arylamino-3-(trifluoromethyl)pyridazines and pyridazino[3,4-b]quinoxalines (as by-products) from 3-aroylmethyl-2-(trifluoromethyl)quinoxalines and hydrazine hydrate

A number of 4-arylamino-3-(trifluoromethyl)pyridazines were obtained in good yields via the novel reaction of 3-aroylmethyl-2-(trifluoromethyl)quinoxalines with an excess of hydrazine hydrate in refluxing n-butanol with or without acetic acid. This reaction is accompanied by the formation of side-products with the pyridazino[3,4-b]quinoxaline skeleton. The possible reaction mechanism was discussed.

Electroluminescence and electron–hole mobility of 6,12-di(thien-2-il)indolo[3,2-b]carbazoles

Novel compounds—substituted indolo[3,2-b]carbazoles (SIC)—which demonstrate semiconducting properties are synthesized. Electroluminescence (EL) is studied in multilayer diode structures based on SIC. The values of hole (6.38 × 10–5 cm2/(V s)) and electron mobilities (1.31 × 10–5 cm2/(V s)) of these electroactive materials are measured. It is estimated that heteroaromatic nuclei are the electron transport centers of SIC molecules.

Reactions of 2-(trifluoroacetyl)chromones with aromatic amines

Aromatic amines reacted with 2-(trifluoroacetyl)chromones as С- or N-nucleophiles, depending on the conditions. When the reaction was performed under solvent-free conditions at 100°С for 12–18 h, they acted as С-nucleophiles and gave bishetarylcarbinols in 21–67% yields, while in refluxing toluene the addition of primary arylamines occurred via the amino group, providing the corresponding hemiaminals (80–86%).

Synthesis and reactivity of 8-aza-5,7-dimethyl-2-trifluoroacetylchromone

Claisen condensation of 3-acetyl-4,6-dimethyl-2-pyridone with methyl 2-methoxytetrafluoropropionate in the presence of LiH in refluxing dioxane gave the corresponding 1,3-diketone, further converted by treatment with conc. H2SO4 to 5,7-dimethyl-2-(1-methoxytetrafluoroethyl)-8-azachromone and 5,7-dimethyl-2-trifluoroacetyl-8-azachromone, which was isolated as hydrate. The first of these azachromones reacted with dinucleophiles at the С-2 atom and the pyrone carbonyl group, while the second reacted at the С-2 atom and trifluoroacetyl group. Based on these compounds, we obtained new trifluoromethylated heterocyclic systems containing a 2-pyridone ring, as well as (8-azachromon-2-yl)(indol-3-yl)carbinols.