Olesya A. Tomashenko

Fe(II)/Et3N-Relay-catalyzed domino reaction of isoxazoles with imidazolium salts in the synthesis of methyl 4-imidazolylpyrrole-2-carboxylates, its ylide and betaine derivatives

Summary A simple approach was developed for the synthesis of methyl 4-imidazolylpyrrole-2-carboxylates from easily available compounds, 5-methoxyisoxazoles and phenacylimidazolium salts under hybrid Fe(II)/Et3N relay catalysis. The products were easily transformed into the corresponding 3-(5-methoxycarbonyl-1H-imidazol-3-ium-3-yl)pyrrol-1-ides, which in turn can be hydrolyzed under basic conditions into the corresponding betaines. A carbene tautomeric form of the 4-methoxycarbonyl-substituted imidazolylpyrrolides was trapped by reaction with sulfur affording the corresponding imidazolethiones under very mild conditions.

Addition of organometallic reagents to nitriles promoted by titanium(IV) isopropoxide as a procedure of synthesis of primary tert-alkylamines

Grignard reagents are able to add twice to nitriles in the presence of titanium(IV) isopropoxide providing primary tert-alkylamines in a fair yield. The conditions and structural features of reagents required for successful reaction were established. A possibility to apply two different organometallic reagents was demonstrated, in particular, the use of organolithium compounds in the second stage.

A new heterocyclic skeleton with highly tunable absorption/emission wavelength via H-bonding

A new heterocyclic system, pyrido[2,1-a]pyrrolo[3,2-c]isoquinoline, was synthesized via Pd-catalyzed intramolecular cyclization of 1-[1-benzyl-2-(2-bromophenyl)-1H-pyrrol-3-yl]pyridin-1-ium bromides. The heterocycles obtained display stimuli responsive fluorescence in solution depending on the nature of the solvent. The strongest blue shift of the emission maxima and growth in luminescence intensity was observed in protic solvents and upon addition of proton donors to solutions of compounds in aprotic solvents. The effect of proton donors on emission characteristics was explained by DFT calculations in terms of H-complex formation with the nucleophilic centres of the molecular skeleton.

NHC as the Guiding Factor in a Copper-Catalyzed Intramolecular C Arylation of Pyrrolylimidazolium Salts: Synthesis of Luminescent Heterotetracyclic Frameworks

3-(2/4-(2-Bromophenyl)-1H-pyrrol-3-yl)-1H-imidazol-3-ium bromides undergo a copper-catalyzed intramolecular direct C arylation under mild conditions to give new heterocyclic frameworks. The cyclizations involve the formation of betaines (imidazoliumylpyrrolides) under basic conditions and the tautomerizaton of the betaines to the corresponding NHCs, which are the reactive species responsible for the selectivity of the arylation via the formation of NHC-Cu complexes. The primary salt arylation products were dehydrohalogenated to obtain the first representatives of 7H-imidazo[2,1-a]pyrrolo[3,2-c]isoquinoline and 1H-imidazo[2,1-a]pyrrolo[3,4-c]isoquinoline heterocyclic skeletons, which were further transformed into thermodynamically more stable 1H- and 6H-tautomers, respectively, by removing of the benzyl-PG. The new heterotetracyclic systems are fluorescent in solutions with high quantum yields.

Synthesis of Pyrrolotriazoloisoquinoline Frameworks by Intramolecular Cu-Mediated or Free Radical Arylation of Triazoles

The cyclization of (2-bromophenyl)pyrrolyl-1,2,4-triazoles via copper-mediated intramolecular direct C-arylation of 1,2,4-triazoles was first accomplished under triazole-NHC control to give unknown fused heterocyclic skeletons, pyrrolo[3,2-c][1,2,4]triazolo[5,1-a] or [3,4-a]isoquinolines. The primary products underwent a triazole ring opening under the basic arylation conditions, providing N-(1H-pyrrolo[3,2-c]isoquinolin-5-yl)cyanamides. The formation of the cyanamides from isomeric pyrrolo[3,2-c][1,2,4]triazolo[3,4-a]isoquinolines involves, besides the triazole ring opening, the unusual migration of the cyano group. Cyanamides can be easily reduced to 1H-pyrrolo[3,2-c]isoquinolin-5-amines, the first NH2-substituted derivatives of 1H-pyrrolo[3,2-c]isoquinoline. An insight into the mechanism of the triazole ring cleavage was achieved by performing a DFT study at the B3LYP/6-31G+(d,p) level. Free radical cyclization of (2-bromophenyl)pyrrolyl-1,2,4-triazoles with TTMSS/AIBN under neutral conditions allows obtaining pyrrolo[3,2-c][1,2,4]triazolo[5,1-a] and [3,4-a]isoquinolines, as well two more new heterocyclic systems, pyrrolo[3,4-c][1,2,4]triazolo[5,1-a] and [3,4-a]isoquinolines, in good yields without triazole ring cleavage. The developed cyclizations provide a concise, atom-economical route to novel fluorescent fused polyheterocycles containing pyrrole and 1,2,4-triazole moieties.

Metalated Ir(III) Complexes Based on the Luminescent Diimine Ligands: Synthesis and Photophysical Study

A series of novel diimine (N∧N) ligands containing developed aromatic [2,1- a]pyrrolo[3,2- c]isoquinoline system have been prepared and used in the synthesis of Ir(III) luminescent complexes. In organic solvents, the ligands display fluorescence which depends strongly on the nature of solvents to give moderate to strong orange emission in aprotic solvents and shows a considerable blue shift and substantial increase in emission intensity in methanol. Insertion of electron-withdrawing and -donating substituents into peripheral phenyl fragment has nearly no effect onto emission parameters. The ligands were successfully used to prepare the metalated [Ir(N∧C)2(N∧N)]+ complexes (where N∧C = phenylpyridine (N∧C-1), p-tolylpyridine (N∧C-2), 2-(benzo[ b]thiophen-2-yl)pyridine (N∧C-3), 2-benzo[ b]thiophen-3-yl)pyridine (N∧C-4), and methyl 2-phenylquinoline-4-carboxylate (N∧C-5)) using standard synthetic procedures. The complexes obtained display moderate to strong phosphorescence in organic solvents; the emission characteristics is determined by the nature of emissive triplet state, which varies substantially with the variations in the structure and donor properties of the C- and N-coordinating functions in metalating ligands. TD-DFT calculations show that for complexes 1, 2, and 4 the emission originates from the mixed 3MLCT/3LLCT excited states with the major contribution from the aromatic moiety of the diimine ligand, whereas in 3 the emissive triplet manifold is mainly located at the N∧C ligand to give structured emission band typical for the ligand centered (LC) excited state. In the case of 5, the phosphorescence may be also assigned to the mixed 3MLCT/3LLCT excited state; however, the major contribution is attributed to the aromatic moiety of the metalating N∧C ligand.

Synthesis, crystal structure, and photophysical properties of dimethyl 7-oxa-2a 1 -azabenzo[ b ]cyclopenta[ pq ]pleiadene-1,2-dicarboxylate – novel fused oxazapolycyclic skeleton

Dimethyl 3-(2-bromophenyl)dibenzo[b,f]pyrrolo[1,2-d][1, 4]oxazepine-1,2-dicarboxylate and its 3,13b-dihydro and 1,2,3,13b-tetrahydro analogs undergo intramolecular cyclization under free radical conditions with the formation of dimethyl 7-oxa-2a1-azabenzo[b]-cyclopenta[pq]pleiadene-1,2-dicarboxylate, the unique representative of pyrrole-fused dibenzo[b,f][1, 4]oxazepines, consisting of six fused rings. This nonplanar oxazapolyheterocycle shows a strong blue emission in dichloromethane.