A 4:1 mixture of 6-chloro-3-(2-phenylethynyl)pyridazine and 3,6-bis(2-phenylethynyl)pyridazine (10.2 g) was stirred in a two-phase mixture of N-aminopyridinium iodide (90% purity; 11 g), benzyltrimethylammonium chloride (1.4 g), sodium hydroxide (5.9 g), dichloromethane (51 ml), and water (51 ml) at ambient temperature for an hour. The reaction mixture was diluted with dichloromethane and water. The organic layer was separated, and the aqueous layer was extracted once with dichloromethane. The combined organic layer was washed with water and brine, dried over anhydrous magnesium sulfate, and concentrated in vacuo. The residue was subjected to column chromatography on silica gel (elution with 25:1 dichloromethane-ethyl acetate) to give 3-(3-chloropyridazin-6-yl)-2-phenylpyrazolo[1,5-a]pyridine (0.72 g) and 3-[3-(2-phenylethynyl)pyridazin-6-yl]-2-phenylpyrazolo[1,5-a]pyridine (0.5 g). Some fractions containing the mixture thereof were subjected to flash column chromatography on silica gel (elution with 50:1 dichloromethane-ethyl acetate) gave an additional product of 3-(3-chloropyridazin-6-yl)-2-phenylpyrazolo[1,5-a]pyridine (0.34 g) and 3-[3-(2-phenylethynyl)pyridazin-6-yl]-2-phenylpyrazolo[1,5-a]pyridine (0.50 g).
