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.

An isoxazole strategy for the synthesis of alkyl 5-amino-4-cyano-1-pyrrole-2-carboxylates - versatile building blocks for assembling pyrrolo-fused heterocycles.

A full atom-economical domino method has been developed for the preparation of alkyl 5-amino-4-cyano-1H-pyrrole-2-carboxylates by transannulation of 5-alkoxyisoxazoles with malononitrile under Fe(ii) catalysis. Alkyl 5-amino-4-cyano-1H-pyrrole-2-carboxylates are excellent building blocks for various annulation reactions, leading to new derivatives of 1H-pyrrolo[1,2-a]imidazole and pyrrolo[2,3-d]pyrimidine. The DFT calculations of mechanistic details of alkyl 5-amino-4-cyano-1H-pyrrole-2-carboxylate formation are presented.

2-Azirine-2-carbonyl Azides: Preparation and Use as N-Heterocyclic Building Blocks.

2-Azirine-2-carbonyl azides, new reactive heterocyclic building blocks, were synthesized in high yield by the reaction of sodium azide with 2-azirine-2-carbonyl chlorides, generated by the Fe(II)-catalyzed isomerization of 5-chloroisoxazoles. 2-(Azidocarbonyl)-1-pyrroles, prepared by the Ni(II)-catalyzed reaction of 2-(azidocarbonyl)-2-azirines with 1,3-diketones, easily undergo the Curtius rearrangement in boiling BuOH to give Boc-protected α-aminopyrroles in high yield. Heating of 2-(azidocarbonyl)-1-pyrroles for a short time in inert solvents leads to the high-yield formation of benzo- and hetero-fused 1-pyrrolo[2,3-]pyridin-6(7)-ones, which are formed via a 6π electrocyclization involving the vicinal aryl or hetaryl substituent and the N═C bond of isocyanate, generated by the Curtius rearrangement of the azidocarbonyl group.

Novel homogeneous photocatalyst for oxygen to hydrogen peroxide reduction in aqueous media.

An isoquinolinium-pyrrole donor-acceptor dyad was found to exhibit photocatalytic activity in oxygen-to-peroxide photoreduction with oxalate as a sacrificial electron donor. The concentration of hydrogen peroxide was shown to reach a plateau of 0.57 mM.

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, 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.

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.