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

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Reaction Steps

4,5-Dichloro-3-hydroxypyridazine (3000 g, 18.18 moles), dihydropyran (1943 g, 23.08 mole), p-toluenesulfonic acid monohydrate (283 g, 1.49 moles) and 16 L of tetrahydrofuran were added to a 50 L round bottomed flask equipped with a heating mantle, reflux condenser and a mechanical stirrer. The mixture was stirred at reflux for 29 h. Additional dihydropyran was added at 6 h (1328 g, 15.79 mol) and at 21 h (780 g, 9.25 moles). The reaction mixture was allowed to cool to room temperature overnight. The mixture was concentrated in vacuo to an oily residue. The residue was taken up in 16 L of ethyl acetate and washed with 2N NaOH (2×6 L). The organic solution was dried (MgSO4) and concentrated in vacuo to give 4,5-dichloro-2-(tetrahydro-2H-pyran-2-yl)-3(2H)-pyridazinone which was a black oily solid which was used without further purification in the next step. The product was purified by filtration through silica gel with ethyl acetate followed by evaporation and recrystallization from ethyl acetate/cyclohexane to give a white solid, mp=74°-76° C.

Provenance & Evidence