Dimethylformamide dimethyl acetal → Methyl 1-[4-(benzyloxy)-2-fluorophenyl]-5-methoxy-4-oxo-1,4-dihydropyridazine-3-carboxylate

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A solution of methyl 2-{[4-(benzyloxy)-2-fluorophenyl]hydrazono}-4-methoxy-3-oxobutanoate (8.46 g, 22.6 mmol) in N,N-dimethylformamide dimethyl acetal (80 mL) was refluxed for 3 h. After cooling to room temperature, the reaction mixture was concentrated under reduced pressure. The residue was diluted with AcOEt, washed with water and brine, dried over MgSO4, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography eluting with THF and recrystallized from hexane/THF to give the title compound (8.12 g, 93% yield) as a white solid: mp 143-144° C.; 1H NMR (300 MHz, CDCl3): δ ppm 3.89 (3H, s), 3.96 (3H, s), 5.12 (2H, s), 6.83-6.91 (2H, m), 7.33-7.44 (5H, m), 7.48-7.54 (1H, m), 7.69 (1H, d, J=2.3 Hz). Anal. Calcd for C20H17FN2O5: C, 62.50; H, 4.46; N, 7.29. Found: C, 62.40; H, 4.59; N, 7.26.

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