N,N,N-trimethyl-1,1-bis(1-methylethoxy)amine → Methyl 1-[2-fluoro-4-(trifluoromethoxy)phenyl]-5-methoxy-4-oxo-1,4-dihydropyridazine-3-carboxylate

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A solution of methyl 2-{[2-fluoro-4-(trifluoromethoxy)phenyl]hydrazono}-4-methoxy-3-oxobutanoate (3.8 g, 11 mmol) and N,N-dimethylformamide diisopropyl acetal (9.5 mL, 54 mmol) in toluene (60 mL) was refluxed for 5 h. The mixture was concentrated under reduced pressure. The residue was diluted with AcOEt, washed with water and brine. The organic layer was dried over MgSO4, filtered and concentrated under reduced pressure. The residue was chromatographed on silica gel (10/90-100/0 AcOEt/hexane) to give the title compound (3.4 g, 86% yield) as pale yellow crystals: 1H NMR (300 MHz, CDCl3): δ ppm 3.91 (3H, s), 3.97 (3H, s), 7.17-7.25 (2H, m), 7.68-7.76 (2H, m).

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