A mixture of 7-bromo-1-(2-methyl-3-nitrophenyl)-3H-pyridazino [4,5-b]indol-4(5H)-one (2.00 g, 5.01 mmol), tributyl(1-ethoxyvinyl)stannane (4.06 mL, 12.02 mmol), dichlorobis(triphenylphosphine)-palladium(II) (0.422 g, 0.601 mmol), and triethylamine (0.908 mL, 6.51 mmol) in 1,4-Dioxane (100 mL) was heated at 95° C. for 24 hr. Upon cooling to room temperature, the mixture was filtered through CELITE®. The filtrate was concentrated under vacuum to dryness. To the residue was added THF (100 mL) and 1 N HCl solution (100 mL), and the mixture was stirred at 60° C. for 1.5 hr. It was concentrated under vacuum to a volume of 100 mL, neutralized with 1 N NaOH solution to pH 4-5, and extracted with ethyl acetate (3×150 mL). The combined, cloudy organic solution was concentrated under vacuum to dryness. To the residue was added hexane (100 mL), and the mixture was stirred at room temperature for 1 hr. The clear solution was decanted and the residue was repeated with this operation for two more times. The solid material was collected by suction filtration to give a crude product (1.98 g, 5.46 mmol, >100% yield) as a beige solid.
