LAUSR

Abstract The synthesis of pyrimido[2,1‐f][1,2,4]triazines was performed in four steps. Compounds obtained by acylation of the starting amino esters of thieno[2,3‐b]pyridines were reacted with various amines. The resulting amino derivatives underwent cyclization in the presence of hydrazine hydrate leading to new aminomethyl derivatives of thieno[3,2‐d]pyrimidines. Further cyclization of the latter resulted to the synthesis of new unique heterocyclic systems: pyrido[3′′,2′′:4′,5′]thieno[3′,2′:4,5]pyrimido[2,1‐f][1,2,4]triazines. The uniqueness of these systems lies in the fact that even the combination of the last two cycles represents a new heterocyclic system.