6-Chloro-3-(trifluoromethyl)-[1,2,4]triazolo[4,3-b]pyridazine (1.8 g, 8.09 mmol), methyl 3-(piperidin-4-yl)-1H-indole-5-carboxylate (2.09 g, 8.09 mmol) and DIPEA (1.55 mL, 8.90 mmol) in DMF (25 mL) were stirred and heated at 80° C. for 1 hour. The resulting mixture was then cooled to ambient temperature and quenched in water (60 mL) to give a precipitate which was collected by filtration, washed sequentially with water, acetonitrile and ether and dried under vacuum to give methyl 3-[1-[3-(trifluoromethyl)-[1,2,4]triazolo[4,3-b]pyridazin-6-yl]piperidin-4-yl]-1H-indole-5-carboxylate (3.29 g, 92%) as a cream solid.
