[F:1][C:2]([F:15])([F:14])[C:3]([N:5]1[CH2:10][CH2:9][C:8]2[CH:11]=[CH:12][O:13][C:7]=2[CH2:6]1)=[O:4].[CH3:16][NH:17][CH3:18].[CH2:19]=O>C(O)(=O)C>[CH3:16][N:17]([CH2:19][C:12]1[O:13][C:7]2[CH2:6][N:5]([C:3](=[O:4])[C:2]([F:1])([F:14])[F:15])[CH2:10][CH2:9][C:8]=2[CH:11]=1)[CH3:18]To a solution of 0.722 g (3.294 mmol) of 6-trifluoroacetyl-4,5,6,7-tetrahydrofuro[2,3-c]pyridine in 50 ml of acetic acid, 0.36 g (4.0 mmol) of 50% aqueous dimethylamine and 0.32 g (4.0 mmol) of 37% aqueous formaldehyde were added, followed by stirring at 100° C. for 1.5 hours. After the solvent was distilled off under reduced pressure, the residue was diluted with water, gently poured into ice-cooled aqueous sodium hydrogen carbonate, and extracted with dichloromethane 3 times. The combined organic layer was dried over anhydrous magnesium sulfate; the solvent was distilled off under reduced pressure. The resulting crude product was purified by silica gel column chromatography (ethyl acetate to ethyl acetate/methanol=4/1) to yield the desired product.
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