3,4-Dimethyl-5,6-disubstited-thieno[2,3-c]pyridazines
(5a-d, 6, and 7) have been synthesized. 5-Amino-3,4-
dimethylthieno[2,3-c]pyridazine-6-carbonitrile (5b) was used as a key intermediate in the synthesis of novel pyrimido[4’,5’:4,5]thieno[2,3-c]pyridazine derivatives (8-12)
and 1,2,4-triazolo[1»,5»:1’,6’]pyrimido[4’,5’:4,5]thieno[2,3-c]pyridazine (14, 15).