Determinative role of ring size and substituents in highly selective synthesis of functionalized bicyclic guanidine and tetra substituted thiophene derivatives based on salt adducts afforded by cyclic thioureas and ketene dithioacetal

Abstract

The condensation of organic salt adducts generated by cyclic thioureas and 2-di(methylsulfanyl)methylenemalononitrile with dialkyl acetylenedicarboxylates selectively leads to either tetrasubstituted thiophenes (2 examples) or hitherto unreported bicyclic guanidine (13 examples) derivatives, with controlling factors being ring size, the substituent on the S-methylisothiourea and the bulk of the substituent on the dialkyl acetylenedicarboxylates. Green solvents, short reaction time; easy purification, high yield and selectivity, are key feature of this protocol in the condensation step. The performances of the reactions in the presence of free-base and a catalyst at room temperature is unprecedented in the synthesis of thiophene frameworks and functionalized bicyclic guanidine scaffolds.