To a solution of ethyl 2-benzyl-4-(4-fluorophenyl)pyrrolo[1,2-b]pyridazine-3-carboxylate (730 mg) in tetrahydrofuran (10 ml) was added N-chlorosuccinimide (260 mg) and the mixture was stirred at 20° C. for 2 hours. The mixture was partitioned between ethyl acetate and water. The organic layer was separated, washed with aqueous sodium thiosulfate, water and brine, dried over magnesium sulfate, and evaporated. The residue was purified by silica gel column chromatograpy eluting with a mixture of toluene and ethyl acetate (10:1) to give ethyl 2-benzyl-7-chloro-4-(4-fluorophenyl)pyrrolo[1,2-b]pyridazine-3-carboxylate (285 mg) as an yellow oil.
