To a solution of 2-(4-chloro-3-trifluoromethylphenyl)-5-methylbenzo[b]-thiophene (0.746 g, 2.28 mmol) in carbon tetrachloride (23 mL) is added N-bromosuccinimide (0.447 g, 2.51 mmol) and 2,2′-azobisisobuyronitrile (AIBN, 0.075 g, 0.46 mmol). The mixture is stirred at 90° C. overnight, and then concentrated. The residue is passed through a pad of silica gel, which is further rinsed with hexanes. The combined organic solution is concentrated in vacuo. The resulting crude product, 5-bromomethyl-2-(4-chloro-3-trifluoromethylphenyl)benzo[b]thiophene, is dissolved in DMF (2 mL) and added to a pre-stirred suspension of β-alanine t-butyl ester hydrochloride (0.828 g, 4.56 mmol) and sodium hydride (0.365 g, 60% dispersion in mineral oil, 9.12 mmol) in DMF (4 mL). The mixture is stirred at room temperature for 4 hours, quenched with water (1 mL) and concentrated in vacuo. The resulting residue is purified by column chromatography (50% to 70% EtOAc/hexanes) to afford 0.79 g (73%) of 3-{[2-(4-chloro-3-trifluoromethylphenyl)benzo[b]thiophene-5-ylmethyl]amino}propionic acid t-butyl ester as a yellow solid.
