Abstract
Apart from its numerous biological activities like antidiabetic, anti-inflammatory, antimicrobial, pyrazine moiety plays an important role in luminescent materials. Its role in luminescent materials is due to its highly electron deficient nature specially when it is in the centre along the mainstay of extended π-conjugated systems. Similarly, new liquid crystalline compounds are being made constantly where the central benzoaromatic moiety is being replaced with the heterocycles including pyrazine due to their more variable nature. Pyrazine derivatives can also be used in supramolecular assemblies due to their efficient hydrogen bonding, protonation and complexation properties. Keeping in view the enormous applications of pyrazine derivatives we planned to synthesize new extended iminobenzoates with pyrazine moieties at the terminal positions. The planned iminobenzoates with terminal pyrazine moieties were prepared following standard procedures. The pyrazine-2-carbohydrazide (1) and 5-methylpyrazine-2-carbohydrazide (2) were prepared by refluxing their methyl esters with hydrazine hydrate in methanol. The esters (3a–3f) were synthesized by reacting 4-hydroxybenzaldehyde with differently substituted acid halides in tetrahydrofuran in the presence of triethyl amine. The target compounds that is, iminobenzoates with the pyrazine moieties at terminal positions (4a–4l), were obtained in good to excellent yields by the reaction of the hydrazides with the esters at reflux. The synthesized compounds were fully characterized using different spectroanalytical techniques including FT-IR, NMR, Mass, elemental analysis and single crystal X-ray diffraction analysis. The paper describes the synthesis of novel iminobenzoates following easy methods while utilizing commercially available starting materials. The synthesized iminobenzoates may possibly be converted to compounds with luminescent and liquid crystalline properties after making suitable changes to the pyrazine moieties. Properly substituted pyrazines on both sides, capable of further suitable extensions, may result in compounds with such properties.
Highlights
Pyrazine belongs to the six membered heterocyclic diazines with two nitrogen in the same ring at 1, 4 positions, the other members being the pyridazine and pyrimidine with the two nitrogens at 1, 2 and 1, 3 positions respectively [1,2,3,4]
Synthesis of the target compounds was carried out according to scheme 1
Further confirmation to the successful synthesis of the esters was made with NMR studies and the data was consistent with the literature known data [33,34,35]
Summary
Pyrazine belongs to the six membered heterocyclic diazines with two nitrogen in the same ring at 1, 4 positions, the other members being the pyridazine and pyrimidine with the two nitrogens at 1, 2 and 1, 3 positions respectively [1,2,3,4]. Both pyrazine and quinoxaline derivatives are quite important due to their crucial roles in natural and synthetic compounds [5,6,7,8,9,10] Apart from their other bioactivities like antidiabetic [11], anti-inflammatory [12], antimicrobial [13] and diuretic [14], pyrazine derivatives, like pyrazinamide, have a vital role in controlling tuberculosis [15]—a life threatening disease. Due to their enormous use in a variety fields of day-today life, chemistry and medicine, luminescent materials are becoming more and more important continuously.
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