Ethyl 2,4-dioxo-5-phenylpiperidine-3-carboxylate → 5-Phenylpiperidine-2,4-dione

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Reaction Steps

Sodium (380 mg, 16.52 mmol) was dissolved in anhydrous ethanol (13 mL) and the resulting solution was treated dropwise with 3-(2-ethoxycarbonyl-acetylamino)-2-phenyl-propionic acid ethyl ester (4.23 g, 13.76 mmol) dissolved in anhydrous toluene (35 mL). The reaction was kept at 80° C. for 1.5 hours. After cooling, the mixture was extracted with water. The aqueous extracts were acidified with 2 N HCl, extracted with ethyl acetate and the organic layers were collected, dried over Na2SO4 and evaporated to dryness to obtain ethyl 2,4-dioxo-5-phenylpiperidine-3-carboxylate (1.73 g, Y=48%) which was used for the next step without further purification. Ethyl 2,4-dioxo-5-phenylpiperidine-3-carboxylate (1.73 g, 6.63 mmol) was dissolved in acetonitrile containing 1% of water (30 mL) and the resulting solution was refluxed for 2 hours. After evaporating to dryness, the crude material was chromatographed on silica gel, eluting with methylene chloride/methanol 92/8, to give the title compound (780 mg, Y=62%) as a solid.

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