General procedure for the synthesis of methyl N-Boc-piperidin-4-one-2-carboxylate from methyl N-Boc-4-hydroxypiperidine-2-carboxylate: to a mixture of oxalyl chloride (15 mL, 30 mmol, 2M solution in dichloromethane) in dichloromethane (100 mL) at -78°C was added DMSO (4.5 mL, 63.4 mmol). After stirring at this temperature for 1 hour, methyl N-Boc-4-hydroxypiperidine-2-carboxylate (2.0 g, 7.71 mmol, dissolved in dichloromethane) was added. After continued stirring for 1 hour, triethylamine (20 mL) was added and the mixture was stirred for another 30 minutes. The reaction mixture was then slowly warmed to -40°C and poured into 10% aqueous sodium bisulfite. The reaction mixture was extracted with ethyl acetate and the combined organic phases were washed with brine and dried over anhydrous magnesium sulfate. The solvent was removed by concentration under reduced pressure and the crude product was purified by fast column chromatography on silica gel to give 1.75 g (88% yield) of the target product as a yellow oil.1H-NMR (CDCl3) δ (ppm): 4.85 (br, d, 1H), 4.02 (m, 1H), 3.61 (s, 3H), 3.00 (br, 1H), 2.75 (m, 2H). 2.44 (br, 2H), 1.43 (br, s, 9H).
