Synthesis, characterization and crystal structure of heterocyclic tetrahydropyrido[4′,3′:4,5]thieno[2,3-d]pyrimidinone derivatives via sequential aza-Wittig/base catalyzed cyclization

Seventeen examples of 7-Benzyl-5,6,7,8-tetrahydropyrido [4′,3′:4,5]thieno [2,3-d]pyrimidin-4(3H) -ones were synthesized by base catalyzed reactions of nucleophilic reagents (aliphatic amines, alcohols or phenols) with carbodiimides 3, which in turn were obtained by the aza-Wittig reaction of iminophosphorane 2 with aromatic isocyanates. The compounds were fully characterized by analytical and spectroscopic techniques (FT-IR, 1H NMR, 13C NMR and MS). Crystal structure determination of three tetrahydropyrido [4′,3':4,5]thieno [2,3-d]pyrimidinone derivatives has been undertaken in order to better understanding the influence of structural modifications upon overall molecular geometry and conformation. 3D supramolecular architectures are formed in the crystals by self-assembly of the molecules via stacking interactions and various hydrogen bonds. Meanwhile, crystal structure of a guanidine intermediate 4a was characterized in order to proclaim the reaction mechanism of the base catalyzed intramolecular cycloaddition.