Sodium Carbonate → (R)-ethyl 3-(tert-butoxycarbonylamino)-4-(3'-chlorobiphenyl-4-yl)butanoate

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A mixture of (R)-ethyl 4-(4-bromophenyl)-3-(tert-butoxycarbonylamino)butanoate (4.89 g, 12.66 mmol), 3-chlorophenylboronic acid (2.97 g, 18.99 mmol), Pd(PPh3)4 (1.463 g, 1.266 mmol) and 2 M aqueous Na2CO3 (12.66 ml, 25.3 mmol) in 1,2-dimethoxyethane (100 ml) is allowed to stir at 95° C. under nitrogen for 3 hours. The reaction mixture is cooled to room temperature and quenched with brine. The two phases are separated. The mixture is extracted twice with ethyl acetate from the aqueous layer. The combined organic layer is washed with brine, dried over MgSO4, filtered, and concentrated under reduced pressure. The obtained residue is purified by silica gel flash column chromatography (heptane/EtOAc=100:0 to 70:30) to give (R)-ethyl 3-(tert-butoxycarbonylamino)-4-(3′-chlorobiphenyl-4-yl)butanoate (3.33 g); HPLC retention time=1.44 minutes (condition B); MS (ES+)=318.26 (m-BOC+2; 100%); 1H NMR (400 MHz, CHLOROFORM-d) δ ppm 1.28 (t, J=7.2 Hz, 3 H) 1.41 (s, 9 H) 2.47 (A of ABX, Jab=15.8 Hz, Jax=5.9 Hz, 1 H) 2.52 (B of ABX, Jab=15.8 Hz, Jbx=5.4 Hz, 1 H) 2.83-2.89 (m, 1 H) 2.95-3.00 (m, 1 H) 4.17 (q, J=7.2 Hz, 2 H) 4.18 (br s, 1 H) 5.07 (br s, 1 H) 7.26-7.37 (m, 4 H) 7.43-7.51 (m, 3 H) 7.55 (br t, J=1.8 Hz, 1 H).

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