Phosphorus oxychloride → Ethyl 4-chloro-6-(2,4-dichlorophenyl)pyrazolo[1,5-a]pyrazine-2-carboxylate

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Reaction Steps

6.86 g (19.5 mmol) of ethyl 6-(2,4-dichlorophenyl)-4-oxo-4,5-dihydropyrazolo[1,5-a]pyrazine-2-carboxylate (Example 11A) were dissolved in 50 ml of phosphoryl chloride and stirred at reflux for 12 h. The reaction mixture was poured into 1.25 l of saturated sodium bicarbonate solution, and solid sodium bicarbonate was added until a pH of 7 had been reached. The solid was filtered off and dissolved in dichloromethane and chromatographed on silica gel (mobile phase cyclohexane/ethyl acetate 10:1). This gave 6.34 g (85% of theory) of the product as a solid.

Provenance & Evidence