Phosphorus oxychloride → 3H-Pyrazol-3-one, 2,4-dihydro-2,5-diphenyl-

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Reaction Conditions

Reaction Steps

A mixture of 2,4-dihydro-2-phenyl-5-hydroxy-3H-pyrazol-3-one (1 g, 5.7 mmol) and POCl3 (1 g, 6.5 mmol) was heated at 100° C. for 4 hours and cooled. The mixture was diluted with ice/water and sodium bicarbonate solution was added (to pH=7). The aqueous layer was extracted with methylene chloride (3×), the organic layer was concentrated in vacuo, and the solid was crystallized from methylene chloride and recrystallized from acetonitrile and methylene chloride. The above solid was purified by column chromatography (silica gel, 6-33% ethyl acetate/hexane) to afford 110 mg of 2,4-dihydro-2-phenyl-5-chloro-3H-pyrazol-3-one (Formula III: R1 =Ph; R2 =Cl; R3 =H) and 56 mg of 1-phenyl-3-hydroxy-5-chloropyrazole as a white solid.

Provenance & Evidence