Synthesis of pyrimido[5″,4″:5′,6′]pyrido[2′,3′:4,5]- thieno[2,3-c]pyridazine and pyridazino[4′3′:4,5]-thieno[3,2-b][1,8]naphthyridine, new tetrahete-rocyclic ring systems

1. Quintela, J.M.
2. Veiga, M.C.
3. Peinador, C.
4. Gonzalez, L.