Paper
Synthesis of Some Novel 3-(4-Pyridinyl)-6-aryl- 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazoles
Published Jan 1, 2011 · A. Mobinikhaledi, N. Foroughifar, Mohammad Bayat
Organic Preparations and Procedures International
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Abstract
It is well known that the thiadiazole nucleus possesses interesting biological properties such as antimicrobial,1–3 antiinflammatory,4–6 antituberculosis,7 antihypertensive,8,9 and anticancer10 activities. Furthermore, the triazole nucleus11–13 and the pyridine14 unit have attracted special attention from chemists due to their attractive biological activities. Incorporating a pyridine ring into active compounds sometimes improves their biological or physiological activities.15 Several heterocycles containing a thiadiazole or triazole moiety have been reported;1–14 however, the synthesis of heterocyclic systems containing a thiadiazole nucleus fused to a pyridine-substituted triazole ring has rarely been reported.16–18 A combination of these three rings may have a variety of structural and biological activities. As a continuation of our studies on the synthesis of thiadiazoles,18 we now report the synthesis of some novel 3-(4-pyridinyl)-6-aryl-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazoles in good yields and purity by a method that recommends itself for its simplicity and convenience. Treatment of 4-pyridinecarboxylic acid hydrazide (1) with base and carbon disulfide in ethanol gave potassium 4-pyridinyldithiocarbazate (2) in good yield. The carbazate was then cyclized to triazole 3 by reaction with hydrazine hydrate under reflux. A variety of aromatic carboxylic acids were subsequently treated with 3 (4:1 molar ratio) in the presence of phosphorus oxychloride to produce the title compounds 4a-j as shown in Scheme 1. The conversion of 3 to 4 proceeded without complication under simple reflux for 8– 10 h, and the products were readily isolated by pouring the reaction mixture onto crushed ice, neutralization with bicarbonate and collection of the resulting solid (40–63% yields). One recrystallization from ethanol-water was sufficient to obtain the analytical samples; with aliphatic carboxylic acids only low yields (10–15%) were obtained. The elemental analyses and spectrometric data for the compounds were consistent with the expected structures. Notably, signals near 1600 cm−1 in the infrared spectra and δ 8.8 in the 1H-NMR spectra indicated the presence of the pyridine moiety in all of the compounds prepared. Our method suggests itself as a useful one for the further investigation of this uncommon combination of heterocyclic units.
Our method for synthesizing novel 3-(4-pyridinyl)-6-aryl-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazoles is simple and convenient, potentially improving biological properties of these compounds.
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