[CH3:1][C:2]1[N:6]2[N:7]=[C:8]([C:11]3[CH:16]=[CH:15][CH:14]=[C:13]([NH2:17])[CH:12]=3)[CH:9]=[CH:10][C:5]2=[N:4][N:3]=1.C(N(C(C)C)CC)(C)C.[C:27](Cl)(=[O:31])[CH2:28][CH2:29][CH3:30].O>ClCCl>[CH3:1][C:2]1[N:6]2[N:7]=[C:8]([C:11]3[CH:12]=[C:13]([NH:17][C:27](=[O:31])[CH2:28][CH2:29][CH3:30])[CH:14]=[CH:15][CH:16]=3)[CH:9]=[CH:10][C:5]2=[N:4][N:3]=1To a solution of 6 g of 3-methyl-6-[3-(amino)phenyl]-1,2,4-triazolo[4,3-b]pyridazine and 5.1 ml diisopropylethylamine in 500 ml dichloromethane was added 3.1 ml of butyryl chloride. This solution was stirred for 12 hours then poured onto 200 ml of water and extracted with 150 ml portions of dichloromethane. The combined extracts were dried, concentrated in vacuo and the solid chromatographed on 500 g silica gel with dichloromethane-methanol (95:5). The fractions containing the desired product were combined, concentrated in vacuo and the solid recrystallized from dichloromethane-hexane to give 5.58 g of white crystals, mp 195°-198° C.
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