[Br:1][C:2]1[C:3](=[O:9])[NH:4][N:5]=[C:6]([Cl:8])[CH:7]=1.[H-].[Na+].[CH3:12][Si:13]([CH3:20])([CH3:19])[CH2:14][CH2:15][O:16][CH2:17]Cl>CN(C=O)C>[Br:1][C:2]1[C:3](=[O:9])[N:4]([CH2:17][O:16][CH2:15][CH2:14][Si:13]([CH3:20])([CH3:19])[CH3:12])[N:5]=[C:6]([Cl:8])[CH:7]=1A 500-mL single-neck round-bottomed flask equipped with a magnetic stirrer was purged with nitrogen and charged with anhydrous DMF (150 mL) and 4-bromo-6-chloro-pyridazin-3(2H)-one (10.0 g, 47.8 mmol). The reaction mixture was cooled to 0° C. and sodium hydride was added. The reaction was stirred at 0° C. for 20 min. After this time, 2-(trimethylsilyl)ethoxymethyl chloride (11.9 g, 71.6 mmol) was added and the cooling bath was removed, and the reaction was stirred at room temperature for 3 h. The reaction was then quenched with saturated aqueous sodium bicarbonate (30 mL). The mixture was extracted with ethyl acetate (2×300 mL). The extracts were dried over sodium sulfate, filtered and concentrated under reduced pressure. The resulting residue was purified by flash chromatography to afford 253a in a 56% yield (9.00 g) as a yellow oil: 1H NMR (300 MHz, CDCl3) δ 8.02 (s, 1H), 5.42 (s, 2H), 3.79 (t, 2H, J=5.4 Hz), 0.96 (t, 2H, J=5.4 Hz), 0.01 (s, 9H).
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