Under 45°C, aqueous ammonia(175 mL) was added to the (1S,3S,6R)-7-oxabicyclo[4.1.0]heptane-3-carboxylate ethyl (17g, 0.1mmol). After TLC confirmed that the reaction was completed, the reaction liquid was vacuum concentrated. Then 175 mL ethanol was added to the reaction. At room temperature, di-tert-butyl dicarbonate (44.0g, 201mmol) dissolved in ethanol would be added to the above mixture. After reaction for 1h, the solid was concentrated in vacuo, and water (300 mL) was added to the mixture.The water layer was extracted with ethanol (300 mL) twice. The organic phase was collected and dried with anhydrous sodium sulfate. After vacuum concentration, the residue was purified by column chromatography on silica gel to obtain (1S,3R,4R)-3-(Boc-aMino)-4-hydroxy-cyclohexanecarboxylic acid ethyl ester.
