Pseudopericyclic dearomative 1,6-cyclization of 1-(2-pyridyl)-2-azabuta-1,3 dienes: synthesis and ring-chain valence equilibria of 4H-pyrido[1,2-a]pyrazines

In this work, we studied 1,6-electrocyclizations of 1-(2-pyridyl)-2-azabuta-1,3-dienes 3 as representatives of 1,4-diazahexatrienes with the C=N bond incorporated in aromatic pyridine system. 2-Azadienes 3 for the study were synthesized by the Rh(II)-catalyzed reaction of triazolopyridines 1 with 2H-azirines 2.This work was done under support of the RSF (grant 19-73-10090) using resources of the Magnetic Resonance Research Centre, Chemical Analysis and Materials Research Centre, Centre for X-ray Diffraction Studies, Computing Centre of the Research Park of St. Petersburg State University

Electoral manipulation and the development of Russia's political system

The allegations of electoral manipulation surrounding Russia's parliamentary election of December 2011 were nothing new. Regional elections in October 2009 resulted in victory for Putin's United Russia, followed by a walkout from the State Duma by the other parliamentary parties, to protest the elections’ conduct. Multi-layered questions surround the role of electoral manipulation for different actors in Russia's political system. Analysis focused on the elections of October 2009 shows that regime, opposition, and regional authorities all have conflicting motivations. For the regime, electoral manipulation helps to secure power and legitimacy, but its uncovering undermines that legitimacy. For the opposition, participation in elections provides an opportunity to both gain electoral representation and to de-legitimise the regime by declaring the ballot flawed. Regional leaders owe their positions to the regime and must balance any obligation to deliver ‘correct’ election results against mixed signals on the nature of that regime and of democracy in Russia

Electrocyclizations of Conjugated Azapolyenes Produced in Reactions of Azaheterocycles with Metal Carbenes

Conjugated azapolyenes (azabuta-1,3-dienes, aza-/diaza-/oxaza-/oxadiazahexa-1,3,5-trienes) are highly reactive in electrocyclization reactions, which makes them convenient precursors for the synthesis of a wide range of four-, five-, and six-membered nitrogen heterocycles that are of relevance for medicinal chemistry. Ring opening reactions of 2H-azirines and azoles containing an N–N or N–O bond, initiated by a transition metal carbene, have become increasingly important in recent years, since they easily allow the generation of azapolyenes with different numbers of double bonds and heteroatoms in various positions. This review summarizes the literature, published mainly in the last decade, on the synthetic and mechanistic aspects of electrocyclizations of azapolyenes generated by the carbene method

Copper(II)-Catalyzed (3+2) Cycloaddition of 2H-Azirines to Six-Membered Cyclic Enols as a Route to Pyrrolo[3,2-c]quinolone, Chromeno[3,4-b]pyrrole, and Naphtho[1,8-ef]indole Scaffolds

A method for the [2+3] pyrroline annulation to the six-membered non-aromatic enols using 3-aryl-2H-azirines as annulation agents is developed in the current study. The reaction proceeds as a formal (3+2) cycloaddition via the N1-C2 azirine bond cleavage and is catalyzed by both Cu(II) and Cu(I) compounds. The new annulation method can be applied to prepare pyrrolo[3,2-c]quinoline, chromeno[3,4-b]pyrrole, and naphtho[1,8-ef]indole derivatives in good to excellent yields from enols of the quinolin-2-one, 2H-chromen-2-one, and 1H-phenalen-1-one series

Azirinium ylides from α-diazoketones and 2H-azirines on the route to 2H-1,4-oxazines: three-membered ring opening vs 1,5-cyclization

Strained azirinium ylides derived from 2H-azirines and α-diazoketones under Rh(II)-catalysis can undergo either irreversible ring opening across the N–C2 bond to 2-azabuta-1,3-dienes that further cyclize to 2H-1,4-oxazines or reversibly undergo a 1,5-cyclization to dihydroazireno[2,1-b]oxazoles. Dihydroazireno[2,1-b]oxazoles derived from 3-aryl-2H-azirines and 3-diazoacetylacetone or ethyl diazoacetoacetate are able to cycloadd to acetyl(methyl)ketene generated from 3-diazoacetylacetone under Rh(II) catalysis to give 4,6-dioxa-1-azabicyclo[3.2.1]oct-2-ene and/or 5,7-dioxa-1-azabicyclo[4.3.1]deca-3,8-diene-2-one derivatives. According to DFT calculations (B3LYP/6-31+G(d,p)), the cycloaddition can involve two modes of nucleophilic attack of the dihydroazireno[2,1-b]oxazole intermediate on acetyl(methyl)ketene followed by aziridine ring opening into atropoisomeric oxazolium betaines and cyclization. Azirinium ylides generated from 2,3-di- and 2,2,3-triaryl-substituted azirines give rise to only 2-azabuta-1,3-dienes and/or 2H-1,4-oxazines