30 g (R)-5-Biphenyl-4-yl-4-tert-butoxycarbonylamino-2-methylenepentanoic acid (2-a, R1=Boc, R2=H, R3=CO2H), prepared according to Example 33 is added to 38.4 g caseium carbonate. Dimethylformamide (50 ml) is then added. Methyl iodide (8.26 ml) is then added and the mixture is stirred for 16 h at room temperature. Water (1200 ml) and isopropyl acetate (120 ml) are added. The phases are separated. The aqueous phase is washed with isopropyl acetate (2×120 ml). The combined organic phases are washed with 20% aqueous sodium chloride solution (180 ml) and then dried (MgSO4). The mixture is concentrated under reduced pressure to afford (R)-5-biphenyl-4-yl-4-tert-butoxycarbonylamino-2-methylenepentanoic acid methyl ester (2-a, R1=Boc, R2=H, R3=CO2Me). 1H NMR (CDCl3): 1.40 (9H), 2.38 (1H), 2.61 (1H), 2.86 (1H), 2.91 (1H), 3.78 (3H), 4.07 (1H), 4.52 (1H), 5.64 (1H), 6.25 (1H), 7.29 (2H), 7.35 (1H), 7.45 (2H), 7.55 (2H), 7.59 (2H).
