To a vial containing tert-butyl-4-[(1R)-1-aminoethyl]benzoate hydrochloride from Step 1 was added N,N-dimethylaminopyridine (3.91 mg, 0.032 mmol), 4-(trifluoromethyl)benzenesulfonyl chloride (0.059 g, 0.24 mmol), N,N-dimethylformamide (2 mL), and triethylamine (0.18 mL, 1.28 mmol). The mixture was stirred at rt for 16 h, after which the solvent was fully evaporated. To the residue was added 1,2-dichloroethane (3 mL), sat. NaHCO3 solution (0.5 mL), and water (0.5 mL). After separation, the aqueous layer was extracted with 1,2-dichloroethane (2×3 mL). The combined organic phases were evaporated to dryness to give (R)-tert-butyl 4-(1-(4-(trifluoromethyl)phenylsulfonamido)ethyl)benzoate as a brown solid. LC-MS: (FA) ES+ 430.
