The developed modular approach to hard-to-reach non-aromatic 3H- and 2H-pyrroles is based on the integration of 2H-azirines and ynamides. Gold-catalyzed [3+2] cycloaddition of 2,2-disubstituted 2H-azirines and ynamides comprises a high...

A one-pot synthesis of tetrasubstituted dihydropyrimidine and pyrimidine derivatives was developed on the basis of UV-LED photolysis of α-azidocinnamates as a key stage.

An efficient one-pot synthesis of imidazo[1,2a]pyridines from 2-bromoazirines and pyridines has been developed. The construction of the bicyclic framework of imidazo[1,2-a]pyridines occurs in two steps through the formation of (2H-azirin-2-yl)pyridinium bromides followed by dehydrobrominative UV light-induced cyclization. The method can also be applied for the synthesis of imidazo[2,1-a]isoquinolines. Unstable in solution, (2H-azirin-2-yl)pyridinium/isoquinolinium bromides were quantitatively converted to stable tetrafluoroborates, which can be cyclized to imidazo[1,2-a]pyridines under UV irradiation in the presence of bromide ions.2H-Azirines due to their diverse reactivity are widely used in the synthesis of various nitrogen heterocycles. 1 A number of effective methods have been developed to selectively transform the azirine ring into other N-heterocycles, such as dihydroazetes, pyrroles, and pyridines, as well as various N,N-and N,O-heterocycles, such as isoxazoles, oxazoles, pyrazoles, oxazines, pyrazines, and pyrimidines. Azirines are also convenient starting materials for the synthesis of various (3,5)-, (3,6)-, (5,6)-, and (6,6)-bicyclic systems, in which they are embedded as the N−CC, NC−C, or CC structural fragments. The annulations of cyclic molecules with azirines have been successfully applied to the preparation of both nonaromatic and aromatic fused heterocycles, the latter being represented in the literature by incomparably fewer examples. Among them, the methods for the preparation of indoles 2 and their benzo-fused derivatives, 3 benzofurans, 4 and 5H-pyrazino-[2,3-b]indoles 5 are most thoroughly developed. One of the efficient approaches to the synthesis of indoles is a catalytic isomerization of 2-arylazirines. It can also be applied to the preparation of azaindoles (diazaindenes) of pyrazolo[1,5a]pyridine and 1H-pyrrolo[2,3-c]pyridine series using 2-(pyridin-2-yl)-6 or 2-(pyridin-4-yl)azirines 7 as starting compounds (Scheme 1, reaction 1). A significant disadvantage of this method is the limited availability of the starting pyridylazirines because they have to be synthesized from nontrivial pyridine-containing precursors. Azirines with a cationic pyridinium substituent, azirinylpyridinium salts, are completely unknown. At the same time, these compounds could be of interest as potential precursors of such an important class of azaindoles as imidazo[1,2-a]pyridines. The imidazo[1,2-a]pyridine derivatives display anticancer, 8 antiviral, 9 anticonvulsant, 10 antimycobacterial, 11 and antileishmanial 12 activity. They also have attracted a great deal of attention

An orthogonal reactivity of diazo compounds toward azirine-2-carboxylic acids, switching with the reaction conditions, is demonstrated. A gold-catalyzed reaction is Nselective and produces 1,3-oxazin-6-ones, whereas a blue light activation leads to O−H insertion products, azirine-2-carboxylic esters. The observed chemodivergence is explained by the metalbound and metal-free carbenes exhibiting different electronic properties in these reactions. In addition, a high antibacterial potential of the 1,3-oxazin-6-ones synthesized is shown.

Diazo compounds display versatile reactivity and therefore are widely used in organic synthesis. Diazo compounds bearing a 2-pyridyl or a related azine moiety on the diazo carbon exist in the form of fused 1,2,3-triazoles. In this short review, we summarize the recent advances in denitrogenative reactions of [1,2,3]triazolo[1,5-a]pyridines (‘pyridotriazoles’) and related fused 1,2,3-triazoles. Over the past decade, there has been a surge of activity in this field, with novel denitrogenative reactions of pyridotriazoles induced by metal compounds, light, and Brønsted and Lewis acids having been devised. As a result, heterocyclic compounds and functionalized α-picolines as well as bio­active molecules have been synthesized. In the review, emphasis is also placed on the mechanisms of the new reactions.1 Introduction2 Ring-Chain Isomerization of Pyridotriazoles3 Metal-Catalyzed Reactions3.1 Rh(II) Catalysis3.2 Rh(III) Catalysis3.3 Cu Catalysis3.4 Pd Catalysis3.5 Catalysis by Other Metals4 Metal-Free Reactions5 Conclusion