To a solution of 4-((1S)-1-{[(benzyloxy)carbonyl]amino}ethyl)benzoic acid (step 1, 3.7 g, 12.4 mmol) and benzyltriethylammonium chloride (3.0 g, 13 mmol) in N,N-dimethylacetamide (100 mL) was added anhydrous potassium carbonate (47 g, 340 mmol) followed by 2-bromo-2-methylpropane (89 g, 650 mmol). The resulting mixture stirred for 24 h at 55° C. After cooling to room temperature, the reaction mixture was poured into cold water (500 mL) under stirring. The resulting solution was extracted with ethyl acetate (500 mL). The organic phase was washed with water (300 mL) and brine (200 mL), dried (sodium sulfate), and evaporated. The residue was purified by flush column chromatography on silica gel (150 g) eluting with hexane/ethyl acetate (3/1) to afford 3.48 g (79%) of the title compounds as white solids: 1H-NMR (CDCl3) δ 7.95 (2H, d, J=8.3 Hz), 7.44–7.24 (7H, m), 5.15–4.99 (3H, m), 4.88 (1H, br.s), 1.58 (9H, s), 1.47 (3H, d, J=7.0 Hz).
