[Br:1][C:2]1[CH:3]=[CH:4][C:5]2[N:6]([N:8]=[C:9](N)[N:10]=2)[CH:7]=1.N([O-])=O.[Na+].C(Br)(Br)[Br:17].ClC(Cl)C(O)=O>[Br-].C([N+](CC)(CC)CC)C1C=CC=CC=1.O.ClCCl>[Br:17][C:9]1[N:10]=[C:5]2[CH:4]=[CH:3][C:2]([Br:1])=[CH:7][N:6]2[N:8]=1
A mixture of 6-bromo-[1,2,4]triazolo[1,5-a]pyridin-2-amine (20.86 g, 97.9 mmol), sodium nitrite (67.6 g, 979 mmol) and benzyltriethylammonium bromide (53.3 g, 196 mmol) in bromoform (1.47 kg, 508 ml, 5.81 mol) was stirred for 30 minutes at 25° C. Then dichloroacetic acid (25.3 g, 16.2 ml, 196 mmol) was added and the mixture was stirred for 20 hours at 25° C. under exclusion of light. 600 ml of water were added to the mixture and stirred for 30 minutes. The mixture was diluted with water and dichloromethane, filtrated over dicalite and the filtrate extracted 3 times with dichloromethane. The organic layers were combined, washed with water, dried over magnesium sulfate, filtrated and evaporated to dryness under reduced pressure. The crude material was purified by flash chromatography in 2 portions over 2×70 g silica columns using dichloromethane/methanol 5% as eluent, affording 2,6-dibromo-[1,2,4]triazolo[1,5-a]pyridine (7 g, 26%) as light brown solid. Mp.: 201° C. MS: m/z=277.7/279.9 (M+H+).
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