[F:1][C:2]([F:18])([F:17])[C:3]([NH:5][CH2:6][CH2:7][C:8]1[CH:13]=[CH:12][C:11]([N+:14]([O-:16])=[O:15])=[CH:10][CH:9]=1)=[O:4].[CH2:19]=O.OS(O)(=O)=O>CC(O)=O>[F:1][C:2]([F:17])([F:18])[C:3]([N:5]1[CH2:6][CH2:7][C:8]2[C:13](=[CH:12][C:11]([N+:14]([O-:16])=[O:15])=[CH:10][CH:9]=2)[CH2:19]1)=[O:4]To the mixture of 2,2,2-trifluoro-N-[2-(4-nitro-phenyl)-ethyl]-acetamide (65 g, 0.25 mole), paraformaldehyde (42.4 g, 0.375 mole, 1.5 eq.) and HOAc (200 mL) in a 1 L round bottom flask equipped with a magnetic stirrer and a ice/water bath was added H2SO4 (300 mL) slowly while maintaining reaction temperature under 40° C. The resulting mixture was stirred for 2 h at 40° C., poured into ice, extracted with EtOAc, washed with water, sat. Na2CO3 and sat. NH4Cl, dried over Na2SO4, filtered and concentrated to give the title ethanone compound. This can be used in the next step without further purification. An analytical sample was obtained through silica gel column chromatography with eluant of CH2Cl2:MeOH (9:1).
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