Study On The Reaction Of Symmetrical Thieno[2,3-b]thiophene O-aminonitrile With Carbonyl Compounds

Thieno[2,3-b]thiophene ring skeleton is a very important structural motif, many compounds containing this core have attracted scientists’ considerable attention because they exhibit broad biological activities such as antiallergenic, antibacterial agents, inhibitors of platelet aggregation, antiglaucoma drugs, anticancer agents, and even HIV protease inhibitors. Furthermore, some compounds of them have also unique optical properties and electron transfer capabilities, and are used as photovoltaic electric materials, such as organic conductor, conductive polymers, dyes, etc.The previous studies of our group showed that the condensations of aromatic o-amino nitrile compounds based on benzene, pyridine cycles with carbonyl compounds can afford not only Friedlander reaction products, but also the new products which contained dihydro pyrimidine ketone structure via PDF conversion. Considering the importance of thieno[2,3-b]thiophene derivatives in both biological and chemical fields and our group’s research on nitrogen heterocyclic compounds, this paper will study the reaction of the symmetrical o-amino aromatic nitrile compounds containing thieno[2,3-b]thiophene skeleton with carbonyl compounds, and the the properties of the products.3,4-diaminothieno[2,3-b]thiophene-2,5-dicarbonitrile was prepared via three components one-pot method using malononitrile, carbon disulfide and bromine acetonitrile as starting materials. The better reaction conditions was acquired by studying some correlative factors such as the catalyst, reaction temperature, solvent, reaction time. The results showed that only PDF conversion occured under base conditions such as in the presence of sodium ethoxide, and the symmetrical tetracycle thieno[2,3-b]thiophene compounds fused pyrimidine ketone derivatives was got; while under anhydrous zinc chloride as catalyst at higher temperature, Friedlander reaction products containing pyridine structure were mainly obtained. Unexpectedly, when we used anhydrous zinc chloride as catalyst at higher temperature, not only the symmetrical Friedlander condensation product 4a was obtained, but the asymmetric across-condensation product 5a from both Friedlander reaction and PDF conversion was also afforded through the reaction of 3,4-diaminothieno[2,3-b]thiophene-2,5-dicarbonitrile with acetone. The structures of all products were confirmed by IR, NMR, and ESI spectra.Furthermore, the crystal structures of compounds 3a, 3h, 4h and 5a were determined by X-ray crystallography, and then UV-VIS spectra and fluorescence emission spectra of the compounds 3,4-diaminothieno[2,3-b]thiophene-2,5-dicarbonitrile, 3,4-diaminothieno-[2,3-b]thiophene-2,5-dicarboxamide, PDF reaction product 3h, and Friedlander reaction product 4h were studied. In addition, the thermal stability properties of compound 3a, 3h, 4h were studied by thermogravimetry analysis(TGA).Finally, we designed the related experiments for study of the reaction mechanism, and a plausible mechanism was proposed.