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 tetraheterocyclic ring systems

Preparation of a number of pyrimido[5 '',4 '':5',6']pyrido-[2',3':4,5]thieno[2,3-c]pyridazine derivatives (4a-h) has been effected by reaction of appropriately heterocyclic aminonitrile precursor (1) and N,N-dimethyldichloromethyleniminium chloride. In addition, pyridazino[4',3':4,5]thieno[3,2-b][1,8]naphthyridines (9a-i), were prepared via the Friedlander synthesis of the N-heteroaromatic carbaldehyde (8) with acyclic, cyclic, heterocyclic or alpha,beta-unsaturated ketones and other active methylene compounds.