p-Toluenesulfonic acid → 5-Iodo-2-(tetrahydro-2H-pyran-2-yl)pyridazin-3(2H)-one

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A mixture of 5-iodo-2H-pyridazin-3-one (8.640 g, 38.92 mmol) in tetrahydrofuran (150 mL) was treated with para-toluenesulfonic acid (1.49 g, 7.86 mmol) and 3,4-dihydro-2H-pyran (8.98 mL, 98.18 mmol). The reaction was stirred at 25° C. for 2 d. After this time, the reaction was filtered. The filtrate was treated with para-toluenesulfonic acid (6 g) and 3,4-dihydro-2H-pyran (9 mL), and the reaction stirred at 25° C. for 6 h. The reaction was concentrated in vacuo, taken up in ethyl acetate (400 mL), washed with a saturated aqueous sodium bicarbonate solution (400 mL), and a saturated aqueous sodium chloride solution. The aqueous layer was extracted with ethyl acetate (300 mL) and was washed with a saturated aqueous sodium chloride solution. The combined organics were dried over sodium sulfate, filtered, rinsed, and concentrated in vacuo. Silica gel column chromatography (AnaLogix, 400 g, 0% to 50% ethyl acetate/hexanes) afforded 5-iodo-2-(tetrahydro-pyran-2-yl)-2H-pyridazin-3-one (2.73 g, 23%) as a clear light brown, viscous oil. The material contained an impurity. However, it was used without further purification.

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