p-Toluenesulfonic acid monohydrate → Ethyl 1-(3-chloropyridin-2-yl)-5-hydroxy-3-(hydroxymethyl)-4,5-dihydro-1H-pyrazole-5-carboxylate

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Reaction Steps

A mixture of ethyl 4-amino-5-hydroxy-2-oxopent-3-enoate (2.5 g, 14 mmol), 3-chloropyridin-2-ylhydrazine (2.07 g, 14 mmol) and p-toluenesulphonic acid monohydrate (2.5 g, 13 mmol) was stirred in 25 ml of acetonitrile at 25° C. for 5 hours. The precipitate was isolated by filtration and the filtrate was concentrated under reduced pressure. The product was purified by column chromatography on SiO2 (eluent: hexane/ethyl acetate). Oil. Yield 4.2 g (90%).

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