33050-32-7

33050-38-3

The general procedure for the synthesis of 3,6-dichloro-[1,2,4]triazolo[4,3-b]pyridazine using 6-chloro-[1,2,4]triazolo[4,3-b]pyridazin-3(2H)-one as starting material is as follows: 6-chloro-[1,2,4]triazolo[4,3-b]pyridazin-3(2H)-one (1 eq.) was added to phosphorochloridic acid (10 eq.). The reaction mixture was heated to reflux and maintained for 20 hours. After completion of the reaction, the mixture was evaporated to dryness. The residue was dissolved in ethyl acetate and washed with saturated aqueous potassium carbonate. The organic layer was dried over anhydrous sodium sulfate, filtered and evaporated to dryness to give Intermediate D in 93% yield. The product was a pale yellow solid.1H NMR (MeOD-d4) data were as follows: δ 7.51 (dd, 1H, J = 9.6Hz, 0.9Hz); δ 8.30 (dd, 1H, J = 9.6Hz, 0.9Hz).