1,2-Dichloroethane → tert-Butyl 2-(4-chlorophenyl)-3-(4-{[(3-ethoxy-3-oxopropyl)amino]carbonyl}phenyl)hexanoate

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Reaction Steps

To a solution of 4-{1-[2-tert-butoxy-1-(4-chlorophenyl)-2-oxoethyl]butyl}benzoic acid (17.8 g, 44 mmol) in DCM (175 mL) at room temperature was added β-alanine ethyl ester hydrochloride (6.6 g, 44 mmol), HOBt (7.85 g, 52.8 mmol), EDC (9.8 g, 53 mmol) and Et3N (30 mL, 220 mmol). After being stirred for 16 hours, the mixture was diluted with DCM then washed with water then saturated NaCl (aq). The organic layer was dried over Na2SO4, filtered, then concentrated. The resulting residue was purified by silica gel chromatography eluting with 0-100% EtOAc/hexanes. The two diastereomeric title compounds were separated by silica gel chromatography eluting with 40% EtOAc/hexanes. The slower-eluting diastereomer is readily resolved to provide enantiopure material by supercritical fluid chromatography on a ChiralPak IA column (3 cm×25 cm) eluting with 50 mL/min of 10% (2:1:3 MeOH:CH3CN:CHCl3) and 90% CO2 at 35° C. and 100 bar.

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