Dimethylformamide dimethyl acetal → Methyl 5-methoxy-4-oxo-1-(2,2,3,3,7-pentafluoro-2,3-dihydro-1,4-benzodioxin-6-yl)-1,4-dihydropyridazine-3-carboxylate

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A mixture of methyl 4-methoxy-3-oxo-2-[(2,2,3,3,7-pentafluoro-2,3-dihydro-1,4-benzodioxin-6-yl)hydrazono]butanoate (6.84 g, 17.2 mmol) in N,N-dimethylformamide dimethyl acetal (68 mL) was heated to reflux for 2.5 h. The mixture was concentrated in vacuo, diluted with brine, extracted with EtOAc, dried over MgSO4, filtered, concentrated in vacuo and purified by column chromatography on silica gel (hexane/EtOAc=50/50 to 0/100 and EtOAc/MeOH=100/0 to 70/30) and on basic silica gel (hexane/EtOAc=80/20 to 0/100 and EtOAc/MeOH=100/0 to 70/30) to yield the title compound (2.58 g, 37% yield) as a pale yellow solid: 1H NMR (DMSO-d6, 300 MHz): δ ppm 3.79 (3H, s), 3.83 (3H, s), 8.01 (1H, d, J=10.2 Hz), 8.16 (1H, d, J=7.2 Hz), 8.58 (1H, s).

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