The general procedure for the synthesis of 4-N-Boc-aminocyclohexanone from 4-(Boc-amino)cyclohexanol was as follows: a dichloromethane solution of dimethyl sulfoxide (6 mL, containing 2.0 mL of dimethyl sulfoxide, 28.2 mmol) was added dropwise to a dichloromethane solution (30 mL) of oxalyl chloride (1.7 mL, 19.5 mmol) over a 10-minute period at -60°C. The dichloromethane solution was stirred for 10 minutes. After dropwise addition, stirring was continued at -60 °C for 10 min. Subsequently, tert-butyl 4-hydroxycyclohexylcarbamate (2.56 g, 11.9 mmol) was added dropwise to a dichloromethane solution (140 mL) over a period of 35 min and the reaction mixture was stirred at -60 °C for 40 min. Next, triethylamine (8.4 mL, 60.3 mmol) was added at -60 °C, after which the reaction mixture was allowed to warm up naturally to room temperature. After completion of the reaction, water was added to the mixture and extracted with chloroform. The organic layer was washed sequentially with saturated aqueous ammonium chloride solution and saturated aqueous sodium chloride solution, and then dried with magnesium sulfate. The solvent was removed by distillation under reduced pressure and the resulting residue was purified by silica gel column chromatography (eluent: chloroform/ethyl acetate) to give tert-butyl 4-oxocyclohexylcarbamate (2.23 g, 87% yield).1H-NMR (DMSO-d6) data were as follows: 1.06-1.20 (4H, m), 1.35 (9H, s), 1.69-1.76 (4H, m). 3.12-3.31 (2H, m), 4.48 (1H, s), 6.64 (1H, d, J = 7.5 Hz).
