A mixture of Boc-D-prolinol (201 mg, 1.0 mmol), p-toluenesulfonyl chloride (400 mg, 2.1 mmol), triethylamine (420 μL, 3.0 mmol), and 4-(dimethylamino)pyridine (12 mg, 0.1 mmol) in dichloromethane (10 mL) was heated at 40° C. for 48 hours, cooled to room temperature, concentrated under vacuum, diluted with ethyl acetate, washed with water and brine, dried (MgSO4), filtered, and concentrated. The residue was purified by column chromatography on silica gel to provide 160 mg (45%) of the desired product.
