p-Toluenesulfonic acid → 4,5-Dichloro-2-(tetrahydro-pyran-2-yl)-2H-pyridazin-3-one

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Reaction Steps

A mixture of 4,5-dichloropyridazin-3-ol (42 g, 250 mmol), 3,4-dihydro-2H-pyran (168 g, 2.00 mol) and p-toluenesulfonic acid (8.8 g, 51 mmol) in tetrahydrofuran (2 L) was heated at reflux for 2 days. After cooling to room temperature, the reaction mixture was concentrated in vacuo and purified by silica gel chromatography (Gradient: 3% to 5% ethyl acetate in petroleum ether). The product was obtained as a white solid. Yield: 42 g, 170 mmol, 68%. 1H NMR (400 MHz, CDCl3) δ 7.84 (s, 1H), 6.01 (br d, J=11 Hz, 1H), 4.10-4.16 (m, 1H), 3.70-3.79 (m, 1H), 1.99-2.19 (m, 2H), 1.50-1.80 (m, 4H).

Provenance & Evidence