Acetyl chloride (193 mL, 2710 mmol) was added dropwise to ethanol (260 mL, 4500 mmol) at −5° C. over 40 min keeping the internal temperature below 30° C. The resulting solution was added over 5 min, at 10° C., to a mixture of ((2S,3S)-7-carbamoyl-1,1-diethyl-3-methoxy-1,2,3,4-tetrahydro-naphthalen-2-yl)-carbamic acid (R)-1-phenyl-ethyl ester (49.0 g, 115 mmol) and ethanol (200 mL). The reaction mixture was stirred at room temperature overnight, and concentrated to ˜100 mL by rotary evaporation. Ethyl acetate (100 mL) was added and the resulting slurry was stirred at 0° C. for 30 min and filtered. The filter cake was washed with ethyl acetate and dried to yield the hydrochloride salt of the title compound (30 g, >99% purity). The volume of the filtrate was reduced almost to dryness. Isopropyl alcohol (20 mL) was added and the resulting thick slurry was stirred for 30 min and filtered. The filter cake was washed with ethyl acetate (2×20 mL) and dried under vacuum overnight to yield additional title compound (5.5 g, >97% purity). 1H NMR (DMSO-d6): δ (ppm) 0.49 (t, 3H), 0.63 (t, 3H), 1.62 (q, 2H), 1.89 (m, 1H), 2.09 (m, 1H), 2.60 (dd, 1H), 3.22 (m, 1H), 3.41 (s, 3H), 3.50 (dd, 1H), 3.82 (q, 1H), 7.19 (d, 1H), 7.31 (br, 1H), 7.70 (d, 1H), 7.71 (s, 1H), 7.98 (br, 1H), 8.15 (br, 3H).
