Azirine-triazole hybrids: selective synthesis of 5-(2-azirin-2-yl)-, 5-(1-pyrrol-2-yl)-1-1,2,3-triazoles and 2-(5-(2-azirin-2-yl)-1-1,2,3-triazol-1-yl)pyridines.

Azirine-triazole hybrids, 1--5-(3-aryl-2-azirin-2-yl)-1-1,2,3-triazoles, were selectively synthesized by reaction of 1-(3-aryl-2-azirin-2-yl)-2-(triphenylphosphoranylidene)ethanones with tosyl and ()-2-benzoylvinyl azides in high yields at rt. The reaction with 2-azidopyridine makes it possible to obtain azirine-triazole-pyridine hybrids, albeit in moderate yields, at 170 °C. The mechanism and selectivity of the reaction of α-carbonylphosphoranes with azides are discussed on the basis of DFT calculations.

Nucleophile-Induced Rearrangement of 2-Azirine-2-carbonyl Azides to 2-(1-Tetrazol-1-yl)acetic Acid Derivatives.

2-Azirine-2-carbonyl azides undergo a rearrangement into derivatives of 2-(1-tetrazol-1-yl)acetic acid when interacting with O- and S-nucleophiles at room temperature. The reaction is catalyzed by tertiary amines or hydrazoic acid. The reaction with primary alcohols and phenols gives alkyl/aryl 2-(1-tetrazol-1-yl)acetates.

Free-radical cyclization approach to polyheterocycles containing pyrrole and pyridine rings.

A wide range of derivatives with new pyrido[2,1-]pyrrolo[3,4-]isoquinoline skeleton was synthesized by free-radical intramolecular cyclization of -bromophenyl-substituted pyrrolylpyridinium salts using the (TMS)SiH/AIBN system. The cyclization provides generally good yields of pyrido[2,1-]pyrrolo[3,4-]isoquinoline hydrobromides having no additional radical-sensitive substituents. The free bases can be obtained from the synthesized hydrobromides in quantitative yield by basification at room temperature.

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

A series of novel diimine (NN) 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.

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.

Synthesis of functionalised azepanes and piperidines from bicyclic halogenated aminocyclopropane derivatives.

A series of 6,6-dihalo-2-azabicyclo[3.1.0]hexane and 7,7-dihalo-2-azabicyclo[4.

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.

Synthesis, Transformations of Pyrrole- and 1,2,4-Triazole-Containing Ensembles, and Generation of Pyrrole-Substituted Triazole NHC.

Unprecedented pyrrole- and 1,2,4-triazole-containing ensembles, substituted 1-(1H-pyrrol-3-yl)-4H-1,2,4-triazol-1-ium bromides and 4-(1H-pyrrol-3-yl)-1H-1,2,4-triazol-4-ium bromides, were prepared from 2H-azirines and triazolium phenacyl bromides using a simple procedure. N-(1H-Pyrrol-3-yl)-N'-benzyltriazolium bromides undergo reductive debenzylation on Pd/C to give substituted 1-(1H-pyrrol-3-yl)-4H-1,2,4-triazoles and 4-(1H-pyrrol-3-yl)-1H-1,2,4-triazoles in high yields. Betaines (triazoliumylpyrrolides) and pyrrolyltriazole NHCs, which are possible products of dehydrobromination of pyrrolyltriazolium salts, have comparable thermodynamic stabilities in nonpolar solvents according to calculations at the DFT B3LYP/6-31G(d) level.

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.

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.

Metal/organo relay catalysis in a one-pot synthesis of methyl 4-aminopyrrole-2-carboxylates from 5-methoxyisoxazoles and pyridinium ylides.

Methyl 4-aminopyrrole-2-carboxylates were synthesized in one-pot mode by the relay catalytic cascade reaction of 5-methoxyisoxazoles with pyridinium ylides by the use of a FeCl2/Et3N binary catalytic system leading to 1-(5-methoxycarbonyl-1H-pyrrol-3-yl)pyridinium salts followed by hydrazinolysis. The approach permits the introduction of a substituent at the pyrrole nitrogen via a nucleophilic reaction of the pyrrolylpyridinium ylide derived from the salt. Catalytic reduction of the ylides gives methyl 4-piperidinopyrrole-2-carboxylates.

A simple approach to pyrrolylimidazole derivatives by azirine ring expansion with imidazolium ylides.

A domino reaction of 2H-azirines with 1-alkyl-3-phenacyl-1H-imidazolium bromides in the presence of Et3N provides a facile route to 1-alkyl-3-(1H-pyrrol-3-yl)-1H-imidazol-3-ium bromides. 1-Benzyl derivatives can be reduced to 1-(1H-pyrrol-3-yl)-1H-imidazoles with HCO2NH4 on Pd/C. The action of KOH on pyrrolylimidazolium salts leads to a new type of stable ylide, 3-(1H-imidazol-3-ium-3-yl)-pyrrol-1-ides, which can, in principle, be in tautomeric equilibrium with the corresponding N-heterocyclic carbene.