General procedure for the synthesis of N-Boc-4,4-difluorocyclohexylamine from 4-N-Boc-aminocyclohexanone: To a solution of 1,1-dimethylethyl (4-oxocyclohexyl) carbamate (1 g, 4.69 mmol, 1 eq.) in dichloromethane (15 mL) was added diethylamino sulfur trifluoride (DAST, 1.05 mL, 7.98 mmol. 1.7 eq.) and the reaction mixture was stirred at room temperature for 15 hours. After completion of the reaction, saturated aqueous sodium bicarbonate solution was added and the resulting two-phase mixture was stirred vigorously for 1 hour. The organic and aqueous layers were separated and the aqueous phase was extracted with dichloromethane. All organic phases were combined, dried with anhydrous magnesium sulfate, filtered and concentrated in vacuum to give 1,1-dimethylethyl (4,4-difluorocyclohexyl) carbamate (D277, 1.03 g, 93% yield) as a beige solid, which could be used in the next step without further purification.
