Semicarbazide Hydrochloride

Typical Procedure:
To a stirred solution of semicarbazide hydrochloride (12.94 g, 116.0 mmol) and sodium acetate trihydrate (0.95 g, 12 mmol) in water (116 mL) is added 1 (2.63 g, 11.6 mmol) at room temperature. Sufficient 95% ethanol is added to bring about a homogenous solution. After stirring at room temperature for 7 h, the reaction mixture is extracted with ethyl acetate. The combined organic phases are washed with brine, dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure. The crude product is purified by silica gel chromatography (ethyl acetate → ethyl acetate : methanol = 9 : 1) to give 2 (2.92 g, 89%) as a white solid.
Next, to a stirred solution of 2 (1.86 g, 6.57 mmol) in dichloromethane (65.7 mL) is added portionwise 95% lead tetraacetate (6.42 g, 13.8 mmol), maintaining the bath temperature at –10 °C After stirring for 1 h at –10 °C, ethyl acetate is added to the reaction mixture, which is allowed to warm to room temperature. Then the mixture is filtered through a Celite pad and concentrated under reduced pressure. The crude product is purified by silica gel column chromatography (hexane : ethyl acetate = 4 : 1) to give 3 (0.83 g, 60%) as a colorless oil.