CS(O)(=O)=O.O=[C:7]1[N:12]([C:13]2[CH:18]=[CH:17][CH:16]=[CH:15][CH:14]=2)N=[C:10](CCC(OCC)=O)[CH2:9][CH2:8]1.[OH-:26].[Na+].[CH2:28]([OH:31])[CH2:29][CH3:30]>>[O:31]=[C:28]([O:31][CH2:28][CH2:29][CH3:30])[CH2:29][C:30]1[C:14]2[C:13](=[CH:18][CH:17]=[CH:16][CH:15]=2)[NH:12][C:7]=1[CH2:8][CH2:9][C:10]([O:31][CH2:28][CH2:29][CH3:30])=[O:26]Methanesulfonic acid (1.15 equiv.) was added to a stirred solution of ethyl 3-(6-oxo-1-phenyl-1,4,5,6-tetrahydropyridazin-3-yl)propanoate from Step 1 in n-propanol (1.1 M). The mixture was stirred overnight at 80° C. The mixture was cooled to room temperature and neutralized with aqueous 1N NaOH (1 equiv.). Final mixture was concentrated under vacuum, diluted with toluene and concentrated again. The residue was purified by column chromatography on silica gel using automatized gradiant pump system CombiFlashRF (Teledyne ISCO) eluting with ethyl acetate/hexane (0:100 to 60:40) to give the title compound (79%) as a brown oil.
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