Studies on the chemical transformations of rotenoids. 5. Synthesis and cytotoxicity of 1,3‐diazepino[5,6‐b]benzofuran and pyridazino[4,5‐b]benzofurans fused with thiazole, imidazole and pyrimidine

Novel benzofuro[2,3‐d]pyridazinium chlorides fused with thiazole 5a, imidazole 5b‐c and pyrimidine 5d‐f were prepared starting from 4‐chloropyridazino[4,5‐b]benzofuran 3a. Treatment of 5b, 5d and 5e with 10% potassium carbonate solution provided the corresponding free bases 6a‐c. Ring closure of methyl rotenononate 1b with amidines proceeded in the presence of sodium methoxide to give 1,3‐diazepino[5,6‐b]benzofuran‐5‐ones 7a‐c. Compound 5d showed cytotoxicity against P388 and L1210 leukemia cells.