Studies on the Chemical Transformations of Rotenoids. IV

Benzofuro[2, 3-d]pyridazin-4(3H)-one (1) was converted into 4-chloro-(3) and 4-ethoxy-benzofuro [2, 3-d]pyridazine (4). Reaction of 1 with phosphorus pentasulfide provided benzofuro-[2, 3-d]pyridazine-4-thione (2), which underwent S-methylation to give the 4-thiomethyl derivative (5). Hydrazinolysis of 2 or 3 proceeded efficiently to give the corresponding 4-hydrazino compound (6). Compound 6 was cyclized with nitrous acid to afford benzofuro[2, 3-d]tetrazolo[1, 5-b]-pyridazine (7), which was alternatively prepared from 3 or 4 with sodium azide.3-Substituted benzofuro[2, 3-d][1, 2, 4]triazolo[4, 3-b]pyridazines (8-12) were prepared by cyclization of 6. Refluxing 6 with ethyl pyruvate in ethanol followed by cyclization in acetic acid provided a novel 4H- benzofuro[2', 3' : 4, 5]pyridazino[3, 2-c][1, 2, 4]triazin-4-one (14).