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The interactions between substituted 5-R-3-(pyridyl-2)-1,2,4-triazines with in situ generated substituted aryne intermediates have been studied. The reaction afforded either inverse demand (ID) aza-Diels-Alder products or 1,2,4-triazine ring rearrangement (domino) products as major ones depending on the nature of both the substituents at the C5 position of the 1,2,4-triazine core or in the aryne moiety. The structures of the key products were confirmed based on X-ray data. Based on the density functional theoretical (DFT) studies of the Diels-Alder transition state geometries, the influence of the nature of arynes on the direction of the 1,2,4-triazine transformation has been proposed.

a b s t r a c tThe reaction between 5-R-6-R 1 -3-(2-pyridyl)-1,2,4-triazines and benzyne generated in situ in toluene under reflux results in the formation of 10-(1H-1,2,3-triazol-1-yl)pyrido[1,2-a]indoles 3 in up to 60% yields instead of the expected 3-R-4-R 1 -1-(2-pyridyl)isoquinolines 2. The crystal structure of product 3c and the proposed mechanism for the formation of 3 are reported.Ó 2013 Elsevier Ltd. All rights reserved.Aryne intermediates are of wide use as versatile tools for the synthesis of various heteroaromatic systems, 1 including photoluminescent intercalators 2 and other physiologically active compounds, such as alkaloids and their carbo-and heterocyclic analogs, 3 and fluorescent sensors for nitroaromatics. 4 At present, most of these compounds can be obtained via the one-step Diels-Alder reaction between various heteroaromatic dienes and cyclic (het)arynes as dienophiles. However, little attention has been given to the reactions of arynes as dienophiles and various cyclic azines as extremely active dienes, the so-called inverse electron demand Diels-Alder reactions. 5 In particular, only a few cases of reactions between 1,2,4-triazines and benzyne to afford isoquinolines in low yields have been described. 6 Moreover, only two cases have been reported for the formation of benzene-annelated analogs of highly promising 2,2 0 -bipyridine-type ligands 7 by the one-step inverse electron demand Diels-Alder reaction between 5-phenyl-3-(2-pyridyl)-1,2,4-triazine and in situ generated benzyne under very harsh conditions: autoclave, toluene, 140°C, 8 or by heating in o-dichlorobenzene at 160°C. 9In addition, we have developed an alternative synthetic approach toward aryl-substituted 1-(2-pyridyl)isoquinolines via the Diels-Alder reaction of 3-(2-pyridyl)-1,2,4-triazines with 1-morpholinocyclohexene followed by aromatization of the resultant tetrahydrosoquinolines. 10Herein we report the results of our study on the reactions of het(aryl)-substituted-1,2,4-triazines with benzyne, which was aimed at the development of a convenient method for the onepot conversion of 1,2,4-triazines into isoquinolines, including benzene-annelated 2,2 0 -bipyridyl ligands. Aryl-substituted 3-(2-pyridyl)-1,2,4-triazines 1a-c were synthesized according to published methods 11 and were used as the starting materials (Scheme 1). Surprisingly, in the reactions between 1a-c and benzyne generated in situ from 2-aminobenzoic acid and isoamyl nitrite 12 in toluene under reflux, we did not observe the formation of the expected pyridyl-isoquinolines 2. Analysis of the 1 H NMR spectra of the obtained products and compound 2a, prepared by an alternative method, 10 did not show any matches, that is, the resonances of the aromatic protons in the products were downfield compared to the similar resonances observed for compound 2a. In addition, according to ESI-mass spectrometry there were four nitrogen atoms in molecules of products 3a-c versus two nitrogen atoms in product 2a. The initial suggestion that the reaction of compound 1 and be...

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A series of new α-(N-biphenyl)-substituted 2,2′-bipyridines were obtained through the combination of the ipso-nucleophilic aromatic substitution of the C5-cyano group, aza-Diels–Alder and Suzuki cross-coupling reactions, starting from 5-cyano-1,2,4-triazines. For the obtained compounds, photophysical and fluorosolvatochromic properties were studied. Fluorophores 3l and 3b demonstrated unexpected AIEE activity, while 3a and 3h showed promising nitroexplosive detection abilities.

Three efficient synthetic approaches towards new azomethine- and terpyridine-containing 2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (diketopyrrolopyrrole, DPP) based polymers, such as P1 and P2, are reported. The first approach involves the Pd-catalyzed synthesis via two- or three-component Suzuki or Stille cross-coupling reaction in solution. The second approach involves Pd-catalyzed Suzuki cross-coupling reaction under ball-milling conditions. And, finally, the third approach involves Pd-free condensation reaction under ball-milling conditions. The newly obtained polymers exhibited absorbance around 700 nm and emission around 900 nm, and, thus, these polymers are considered to be NIR-fluorophores.