Reaction Steps
racemic-1,1-Dimethylethyl[(1S,2R)-2-(hydroxymethyl)cyclohexyl]carbamate. racemic-[(1R,2S,5S)-2-Amino-5-phenylcyclohexyl]methanol hydrochloride (800 mg, 4.82 mmol) was dissolved in MeOH (40 mL) and bis(1,1-dimethylethyl)dicarbonate (1.16 g, 5.30 mmol) and triethylamine (4 mL, 28.92 mmol) were added and the mixture was stirred 18 hours at ambient temperature. The solvents were removed under reduced pressure, ethyl acetate and aqueous saturated sodium bicarbonate were added and the product was extracted with ethyl acetate. The combined organics were dried over sodium sulfate and the solvents were removed under reduced pressure. Purification by silica gel chromatography (9:1 hexanes:ethyl acetate to ethyl acetate gradient elution) gave 1,1-dimethylethyl racemic-[(1S,2R)-2-(hydroxymethyl)cyclohexyl]carbamate (934 mg, 85%) as a white solid. 1H NMR (CDCl3) δ 4.87 (m, 1H), 4.03-3.95 (m, 2H), 3.26 (m, 1H), 3.15 (m, 1H), 1.73-1.48 (m, 5H), 1.38 (s, 9H), 1.27-1.15 (m, 3H), 0.887 (m, 1H). b) racemic-1,1-Dimethylethyl[(1S,2R)-2-Formylcyclohexyl]carbamate. To a solution of dimethylsulfoxide (0.2 mL, 2.88 mmol) in dichloromethane (3 mL) at −78° C. was added oxalyl chloride (0.72 mL, 1.44 mmol) dropwise. The mixture was stirred 10 minutes and racemic-1,1-dimethylethyl [(1S,2R)-2-(hydroxymethyl)cyclohexyl]carbamate (220 mg, 0.961 mmol) in dichlormethane was added dropwise and stirred 10 minutes. Triethylamine (0.53 mL, 3.84 mmol) was added slowly and the reaction was stirred at −78° C. for one hour and allowed to warm to ambient temperature. Water was added and product was extracted with dichloromethane. The combined organics were washed with brine and dried over sodium sulfate. Removal of solvents under reduced pressure afforded racemic-1,1-dimethylethyl[(1S,2R)-2-formylcyclohexyl]carbamate (223 mg, quantitative) as a yellow oil. 1H NMR (CDCl3) δ 9.61 (s, 1H), 5.19 (m, 1H), 3.88 (m, 1H), 2.61 (m, 1H), 1.85 (m, 1H), 1.63-1.49 (m, 4H), 1.37-1.16 (m, 12H). c) racemic-1,1-dimethylethyl ((1S,2S)-2-{[(2-Methylpropyl)amino]methyl}cyclohexyl)carbamate. racemic-1,1-Dimethylethyl [(1S,2R)-2-formylcyclohexyl]carbamate (223 mg, 0.982 mmol) was dissolved in dichloroethane and 2-methylpropyl)amine (0.15 mL, 1.47 mmol) and sodium triacetoxyborohydride (290 mg, 1.37 mmol) were added and the reaction was stirred at ambient temperature for 18 hours. Aqueous sodium bicarbonate was added and the product was extracted with dichloromethane. The combined extracts were dried over sodium sulfate and the solvents were removed under reduced pressure. Purification by silica gel chromatography (dichloromethane to 1% ammonium hydroxide 19% methanol 80% dichloromethane gradient elution) afforded racemic-1,1-dimethylethyl ((1S,2S)-2-{[(2-methylpropyl)amino]methyl}cyclohexyl)carbamate (112 mg, 40%) as a clear colorless oil. 1H NMR (CDCl3) δ 6.06 (br s, 1H), 3.76 (br s, 1H), 2.63 (m, 1H), 2.43-2.37 (m, 2H), 2.25 (m, 1H), 1.81 (m, 1H), 1.71-1.59 (m, 3H), 1.44-1.32 (m, 14H), 1.27-1.19 (m, 2H), 0.866 (m, 6H). d) racemic-(1S,2S)-2-{[(2-Methylpropyl)amino]methyl}cyclohexanamine hydrochloride.
