Synthesis of thieno[2,3-b]thiophene fused pyrimidine derivatives via sequential conversion of 3,4-diaminothieno[2,3-b]thiophene-2,5-dicarbonitrile with carbonyl compounds

A simple, straightforward synthesis of thienothiophene fused pyrimidine derivatives has been developed by the heterocondensation of symmetric thieno[2,3-b]thiophene o-aminonitrile with carbonyl compounds under different catalytic conditions. Furthermore, a novel unsymmetric thiophthene skeleton compound was also obtained via the intramolecular cross-conversion of the Friedländer transformation and the Pinner-Dimroth-in-Friedländer reaction under the catalyst of Lewis acid. The structures of products were confirmed by IR, NMR, and ESI spectra and X-ray crystallography. A plausible mechanism was proposed.